GTA
All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: rsterne on June 14, 2017, 08:36:09 PM
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I have had a few guys ask about the idea of making a 6mm PCP, and it has aroused my curiousity, so I did some research.... I knew that LW made barrels in various twists (8, 9, 10, & 14") but I had never seen one in TJ's list, so I contacted Mike and it turns out that he has a mandrel to make them with 0.237" lands and 0.243" grooves, with a 10" twist.... They can be made in 1/2" and 9/16" OD, and he has a 9/16" in stock.... Then I started looking around for moulds to cast bullets, and I found these....
The first one is a Lyman 225107, interpolated out to a larger diameter by NOE.... It says it weighs 46 gr., but they currently have no stock in the store....
(http://i378.photobucket.com/albums/oo221/rsterne/NOE%20Bobs%20Boattails/6mm%20NOE%2046%20gr_zpsbltyoemh.jpg) (http://s378.photobucket.com/user/rsterne/media/NOE%20Bobs%20Boattails/6mm%20NOE%2046%20gr_zpsbltyoemh.jpg.html)
The second one is a scaled down Lyman 257420, done at the request of Jack Bowman (Scandalous Airguns).... Aresenal have this mould available to order, listed at 60 gr....
(http://i378.photobucket.com/albums/oo221/rsterne/NOE%20Bobs%20Boattails/6mm%20Arsenal%2060%20gr_zpst0kla0pm.jpg) (http://s378.photobucket.com/user/rsterne/media/NOE%20Bobs%20Boattails/6mm%20Arsenal%2060%20gr_zpst0kla0pm.jpg.html)
The third one is listed as a 73 gr., and is also out of stock at NOE....
(http://i378.photobucket.com/albums/oo221/rsterne/NOE%20Bobs%20Boattails/6mm%20NOE%2075%20gr_zpsrkrxr4gl.jpg) (http://s378.photobucket.com/user/rsterne/media/NOE%20Bobs%20Boattails/6mm%20NOE%2075%20gr_zpsrkrxr4gl.jpg.html)
I scaled down my .257 cal 78 gr. BBT, and have sent the drawing to Al to add to the AirGun Discussion Section on the NOE Forum.... It looks like this....
(http://i378.photobucket.com/albums/oo221/rsterne/NOE%20Bobs%20Boattails/NOE%20243%20cal%2065%20gr_zpsn1sevxzd.jpg) (http://s378.photobucket.com/user/rsterne/media/NOE%20Bobs%20Boattails/NOE%20243%20cal%2065%20gr_zpsn1sevxzd.jpg.html)
All of these should work just fine in Mike's 10" twist barrel.... According to my "lofty goal" PCP spreadsheet, with a 24" barrel at 3000 psi, and bore-sized porting, it should be possible to hit about 139 FPE.... In reality, that means you could probably do that with a 28" barrel, with the gun tuned to the max.... It should put the mid 900's within reach with my 65 gr. BBT with a 24-28" barrel at 3000 psi.... In other words, without going to ridiculous barrel lengths or pressures, any of the above bullets should be usable.... with the 46 gr. only requiring maybe 2200 psi or so....
Anyways, I thought I would throw this idea out there for everyone to chew on.... If there is enough interest, I'm sure we could get Al to put the BBT in a Group Buy, and the others into Inventory Runs.... I already started a thread at NOE to express your interest in the 46 gr. in hopes of getting an Inventory Run started....
Bob
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Very interesting. Could you list the pros and cons of this caliber when compared to .257 and .224? That Arsenal copy of 257420 sounds like a sure bet for a long range bullet.
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I`m not ACCLAIMED with this type of ammo.. What would be the benefit of barel change and molding this type of projectile??
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Very interesting. Could you list the pros and cons of this caliber when compared to .257 and .224? That Arsenal copy of 257420 sounds like a sure bet for a long range bullet.
x2
And if this Beeman Chief as some "stuff" too it, could be an even less daunting task for the non-machinist to make a nice little shooter. I personally like the idea of reach those somewhat higher FPEs with smaller projectiles. Possibly another simple conversion on the Airforce platform as well??? Options, like options ;)
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I could write a long article and end up saying very little.... in reality, there is no overwhelming reason to choose 6mm (.243 cal) over either .224 cal or .257 cal.... much like there is no overwhelming reason for .20 cal pellets, compared to .177 or .22 cal.... All the arguments about why one caliber is better than another are a matter of which compromise you prefer.... In the broadest, and most general terms, consider the following....
Larger calibers make more FPE, but require more air to do so (their efficiency is marginally better, however).... More FPE makes them more suitable for larger game....
Larger caliber bullets have a higher Sectional Density, for any given shape, so for that shape, have a higher Ballistics Coefficient (because of the square/cube rule)....
The higher the SD, the longer the barrel, or the higher the pressure, it takes to achieve a given velocity.... important if we want to stay in the 900 fps range....
To achieve 950 fps, using 3000 psi and a 24" barrel, requires (with current technology, on air) the SD to be under 0.17.... the further under, the easier it is to achieve....
Conversely, as we go to a smaller caliber, for a given SD, bullets get longer and slimmer, and therefore tend towards less form drag, and a better BC....
For target shooting, or Varmint hunting, at long range, a high BC is better.... and in addition the FPE requirements are relatively low.... favouring a smaller caliber....
Wind drift (when shooting in a limited velocity range such as in the 900s) is almost entirely dependant on the BC.... higher BC equals less drift....
Wind drift is minimized, at ranges out to 200 yards or so, when the muzzle velocity is around 900 fps.... and in fact is as low as the same bullet at about 3000 fps....
There are probably more things I could add to that list, but looking at those, caliber choice, most importantly, depends on the use.... If the goal is to shoot small game, or targets, at long range.... and being limited by the physics to optimum velocities in the 900s (low 1000s at most).... then you can make an overwhelming argument that the smaller the caliber, the better.... provided you have enough downrange FPE to engage your intended target.... This means that all things being equal, a .224 cal would be hard to beat for most Varmint airgunning.... So, why is the .257 cal the "go to" caliber for this task (I don't think anyone would currently argue that).... IMO, the biggest reason is the availability of suitable components.... ie barrels and bullets that work together....
Probably the most widely used combination in the .257 is the Lyman 257420 (SD = 0.158), in a 14" twist barrel, shooting between 950-1050 fps.... It casts at about 73 gr. in pure lead, is deadly accurate, and within that velocity range has 145-180 FPE of energy at the muzzle, and maintains about 115-130 FPE of that at 100 yards.... It hits hard, but requires a pretty powerful gun to get into the mid 900s, things like a modified Condor running relatively long-ish barrels and/or high-ish pressures.... There are more powerful PCPs, shooting even heavier bullets, in order to get a better BC, the most notable being the 92 gr. "Noble" (named after our own dyotat100).... but with an SD of over 0.20 that requires even more push (longer barrel and/or more pressure) to achieve similar velocities.... One could make the argument that the additional FPE required is wasted on small targets, although if Predator hunting is your forte, it could be just the ticket....
If we look at .224 cal, it is sadly neglected and under-represented, for basically one reason.... Most of the barrels are too slow a twist to stabilize the longer projectiles we would like to use.... The most common barrel available is only a 14" twist, which limits your bullet choice to under about 50 gr.... While pushing that weight at 950 fps gives you 100 FPE, adequate for most work, and equalling a subsonic .22LR, we can't use those specialized, long lean bullets we would like to.... In fact, there are VERY few moulds available in .224 cal (that will work in a 14" twist), the best out there at present is probably the Lyman 37 gr. 225107 (SD = 0.105).... Pushed at 950 fps, you get 74 FPE at the muzzle, and are down to about 54 FPE at 100 yards.... To get a bullet with an SD comparable to the 73 gr. 257420, we end up requiring 55 gr.... which then dictates a twist rate of about 10".... Yes, you can get that from LW, if you want a barrel with a 1.26" OD, but TJ's, for example, have nothing faster than a 12 twist, and that is .223 cal.... So, the .224 cal remains neglected in airguns, from lack of a readily available combination of barrels and bullets.... Also, .22 cal bullets are just that much harder to cast well than .25 cal....
The reason I looked at 6mm was to see if there was a combination of "stuff" that would make sense for what we "need" for the job of Varmint control and target shooting.... I was surprised to find that there is pretty much an ideal combination sitting there waiting for somebody to put it together.... TJ's have a 10" twist barrel that is 0.243" groove and 0.237" land.... and Arsenal sell moulds for the "Bowman" 60 gr. (SD = 0.145), which is a scaled down 257420.... If there is any bullet that stands a great chance of working well, that would be my bet.... While it would work fine in a 14" twist, it won't be turning too fast in that 10".... and the faster twist allows for heavier, longer bullets to be used as well.... if and when the caliber develops a following, and transitions to higher power airguns.... With the SD, you should be able to drive it into the mid 900s with a 24" barrel at 3000 psi, and still maintain reasonable efficiency.... Another possibility is the 73 gr. NOE (SD = 0.177), which needs a 12" or faster twist, and a bit more power to drive it.... Then, of course, I looked at designing a BBT, and scaled down my .257 cal 78 gr. and came up with a 65 gr. bullet (SD = 0.157) with a design twist of 11".... For those comtemplating a less powerful build, the NOE 46 gr. (SD = 0.111) would provide the opportunity to use a regulated PCP at lower pressures, without the need to have too long a barrel....
Make no mistake, a 6mm shooting the 60 gr. Bowman is still a powerful PCP.... At 950 fps, it will have 120 FPE at the muzzle, and about 90 FPE at 100 yards.... just about exactly duplicating the power of a .22LR.... A HP version would be devastating at those power levels, without being overkill.... and would use significantly less air than a .257 cal of comparable performance (wind drift and trajectory).... Is it necessary, no?.... Is it "better" than a .224 shooting a 55gr. pill would be for Varmint hunting, no not really, although a bit more FPE.... However, it would be a lot of fun, not too hard to put together from available components, and would certainly do the job.... Do we need any more reasons to try it?....
Bob
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Hmmm There is plenty of choise of blank barrels at .223/.224 if You willing put some money on table. Green mountain, Bartlein ,Shilen , Hart ,Douglas etc.. Why always TJ ? Just my 2 c
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$$$ .... I don't have much of it.... plus availability in Canada.... ::)
Bob
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I could write a long article and end up saying very little.... in reality, there is no overwhelming reason to choose 6mm (.243 cal) over either .224 cal or .257 cal.... much like there is no overwhelming reason for .20 cal pellets, compared to .177 or .22 cal.... All the arguments about why one caliber is better than another are a matter of which compromise you prefer.... In the broadest, and most general terms, consider the following....
Larger calibers make more FPE, but require more air to do so (their efficiency is marginally better, however).... More FPE makes them more suitable for larger game....
Larger caliber bullets have a higher Sectional Density, for any given shape, so for that shape, have a higher Ballistics Coefficient (because of the square/cube rule)....
The higher the SD, the longer the barrel, or the higher the pressure, it takes to achieve a given velocity.... important if we want to stay in the 900 fps range....
To achieve 950 fps, using 3000 psi and a 24" barrel, requires (with current technology, on air) the SD to be under 0.17.... the further under, the easier it is to achieve....
Conversely, as we go to a smaller caliber, for a given SD, bullets get longer and slimmer, and therefore tend towards less form drag, and a better BC....
For target shooting, or Varmint hunting, at long range, a high BC is better.... and in addition the FPE requirements are relatively low.... favouring a smaller caliber....
Wind drift (when shooting in a limited velocity range such as in the 900s) is almost entirely dependant on the BC.... higher BC equals less drift....
Wind drift is minimized, at ranges out to 200 yards or so, when the muzzle velocity is around 900 fps.... and in fact is as low as the same bullet at about 3000 fps....
There are probably more things I could add to that list, but looking at those, caliber choice, most importantly, depends on the use.... If the goal is to shoot small game, or targets, at long range.... and being limited by the physics to optimum velocities in the 900s (low 1000s at most).... then you can make an overwhelming argument that the smaller the caliber, the better.... provided you have enough downrange FPE to engage your intended target.... This means that all things being equal, a .224 cal would be hard to beat for most Varmint airgunning.... So, why is the .257 cal the "go to" caliber for this task (I don't think anyone would currently argue that).... IMO, the biggest reason is the availability of suitable components.... ie barrels and bullets that work together....
Probably the most widely used combination in the .257 is the Lyman 257420 (SD = 0.158), in a 14" twist barrel, shooting between 950-1050 fps.... It casts at about 73 gr. in pure lead, is deadly accurate, and within that velocity range has 145-180 FPE of energy at the muzzle, and maintains about 115-130 FPE of that at 100 yards.... It hits hard, but requires a pretty powerful gun to get into the mid 900s, things like a modified Condor running relatively long-ish barrels and/or high-ish pressures.... There are more powerful PCPs, shooting even heavier bullets, in order to get a better BC, the most notable being the 92 gr. "Noble" (named after our own dyotat100).... but with an SD of over 0.20 that requires even more push (longer barrel and/or more pressure) to achieve similar velocities.... One could make the argument that the additional FPE required is wasted on small targets, although if Predator hunting is your forte, it could be just the ticket....
If we look at .224 cal, it is sadly neglected and under-represented, for basically one reason.... Most of the barrels are too slow a twist to stabilize the longer projectiles we would like to use.... The most common barrel available is only a 14" twist, which limits your bullet choice to under about 50 gr.... While pushing that weight at 950 fps gives you 100 FPE, adequate for most work, and equalling a subsonic .22LR, we can't use those specialized, long lean bullets we would like to.... In fact, there are VERY few moulds available in .224 cal (that will work in a 14" twist), the best out there at present is probably the Lyman 37 gr. 225107 (SD = 0.105).... Pushed at 950 fps, you get 74 FPE at the muzzle, and are down to about 54 FPE at 100 yards.... To get a bullet with an SD comparable to the 73 gr. 257420, we end up requiring 55 gr.... which then dictates a twist rate of about 10".... Yes, you can get that from LW, if you want a barrel with a 1.26" OD, but TJ's, for example, have nothing faster than a 12 twist, and that is .223 cal.... So, the .224 cal remains neglected in airguns, from lack of a readily available combination of barrels and bullets.... Also, .22 cal bullets are just that much harder to cast well than .25 cal....
The reason I looked at 6mm was to see if there was a combination of "stuff" that would make sense for what we "need" for the job of Varmint control and target shooting.... I was surprised to find that there is pretty much an ideal combination sitting there waiting for somebody to put it together.... TJ's have a 10" twist barrel that is 0.243" groove and 0.237" land.... and Arsenal sell moulds for the "Bowman" 60 gr. (SD = 0.145), which is a scaled down 257420.... If there is any bullet that stands a great chance of working well, that would be my bet.... While it would work fine in a 14" twist, it won't be turning too fast in that 10".... and the faster twist allows for heavier, longer bullets to be used as well.... if and when the caliber develops a following, and transitions to higher power airguns.... With the SD, you should be able to drive it into the mid 900s with a 24" barrel at 3000 psi, and still maintain reasonable efficiency.... Another possibility is the 73 gr. NOE (SD = 0.177), which needs a 12" or faster twist, and a bit more power to drive it.... Then, of course, I looked at designing a BBT, and scaled down my .257 cal 78 gr. and came up with a 65 gr. bullet (SD = 0.157) with a design twist of 11".... For those comtemplating a less powerful build, the NOE 46 gr. (SD = 0.111) would provide the opportunity to use a regulated PCP at lower pressures, without the need to have too long a barrel....
Make no mistake, a 6mm shooting the 60 gr. Bowman is still a powerful PCP.... At 950 fps, it will have 120 FPE at the muzzle, and about 90 FPE at 100 yards.... just about exactly duplicating the power of a .22LR.... A HP version would be devastating at those power levels, without being overkill.... and would use significantly less air than a .257 cal of comparable performance (wind drift and trajectory).... Is it necessary, no?.... Is it "better" than a .224 shooting a 55gr. pill would be for Varmint hunting, no not really, although a bit more FPE.... However, it would be a lot of fun, not too hard to put together from available components, and would certainly do the job.... Do we need any more reasons to try it?....
Bob
NOPE!! I see your point very clearly but the need I a niche that most hunters will just go with powder burners for convenience.. Air rifles are more of general use... But dont get me wrong!!! I see your point and the arguments you give are legitimales... The practicality of an Air Force Condor is filling the blank in that niche and the HARD WORK you make in the calculations could IMPROUVE the Condor platform just as you pointed out.. I know Bob that is guy like you that have been PUSHING THE ENVELOPPE of airgunning and make manufacturers IMPROUVE their products..
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I want a .244/6mm but I want it like the old .244 Remington 1:12 twist and keep watching for an old barrel for a good price... why...? because each caliber will have a lightest-heaviest(more about round length and twist in that range) that they do well with...
So in .25 the 40g BBT at 60 fpe is traveling about 825 fps... gives decently flat trajectory only takes a bit of modding to get there probably just a 10# spring... It may do well from 500fps up to 1050 fps or it may have a sweet spot somewhere in that fps range...
but with my 60 fpe 19" barrel Mrod I need to hope the round/barrel has a broad enough sweet spot that it gets into it by 60fpe/825fps...( I would rather be at 900-1000 fps though...
So for a cast .25 the lightest round you can get is the swagged .25 from Nielsen at about 34g and hollow point 40g BBT at about 37g any thing less would not have enough bearing length to be stable in the barrel... other than wasp waist draggy lower B.C. pellets...
while the 40g BBT (I think of it almost like an improved SWC) has a better B.C. than pellets it is not all that good for a bullet in .25 the 50g will be much better B.C. wise... but you need more mods to get to 80-100 fpe for it... say a 28" barrel instead of 19"...and you can go heavier if you have the twist and power for it... BUT how big of a tank do you have and do you hand pump... and how long of a barrel are you willing to use...
So for a number of reasons my choice is to stay around 60 fpe with a near stock Mrod...
in .22 I have the 30g BBT and 22" to 28" barrels... 27"-28" barrel should get me to about 60 fpe... But honestly want about a 24" barrel max for a hunting rig... and at that barrel length a .244 of 40-45 grains and a near stock Mrod will get there... and have a better B.C. than the 40g .25 which only needs a 19" barrel to get to 60 ish fpe...
And that is why a .244 Remmy Mrod is very appealing to me... Well suited for hand pumped near stock Mrod without having to have an excessively long barrel...
Just do not have the Green stamps for it right now...
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The 46 gr. NOE 245107 bullet would be near ideal for that project, Kirby.... You should add your name to the list of those interested in an Inventory Re-run on the NOE website....
Bob
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The 46 gr. NOE 245107 bullet would be near ideal for that project, Kirby.... You should add your name to the list of those interested in an Inventory Re-run on the NOE website....
Bob
I would but My Oldest Daughter is getting married on the 28th and I will be BROKE for the next 6-months...
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It's not a commitment to purchase.... and it might take that long to get it into the Inventory Run anyways.... http://noebulletmolds.com/smf/index.php/topic,2125.0.html (http://noebulletmolds.com/smf/index.php/topic,2125.0.html)
Bob
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I could write a long article and end up saying very little.... in reality, there is no overwhelming reason to choose 6mm (.243 cal) over either .224 cal or .257 cal............ C
Do we need any more reasons to try it?....
Bob
I think you summed it up quite well. And why TJ for me, great results with several of their barrels, value, and ease of fitting it to modifications that is recommended by the folks who do the work. I think its neat to tinker with various calibers even if for just comparing same platform in different calibers.
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The other thing I like about TJ's barrels is the light weight.... I can stiffen them up with a Carbon Fibre sleeve and end up with a barrel that is stiffer than a typical PB barrel at a fraction of the weight.... Virtually all of the PB barrels I have seen are 1.20 - 1.26" in diameter, and must be turned down to the profile you need.... Even so, they weigh a LOT, even ones that are thinned down to 9/16" or so at the muzzle.... Why start with a barrel that is intended for 50,000+ psi when we only need 1/10th of that strength?....
Bob
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The other thing I like about TJ's barrels is the light weight.... I can stiffen them up with a Carbon Fibre sleeve and end up with a barrel that is stiffer than a typical PB barrel at a fraction of the weight.... Virtually all of the PB barrels I have seen are 1.20 - 1.26" in diameter, and must be turned down to the profile you need.... Even so, they weigh a LOT, even ones that are thinned down to 9/16" or so at the muzzle.... Why start with a barrel that is intended for 50,000+ psi when we only need 1/10th of that strength?....
Bob
Unfortunately TJ liners are unobtainium here in Europe so we need to use LW blanks as our low cost option :(
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Make no mistake, a 6mm shooting the 60 gr. Bowman is still a powerful PCP.... At 950 fps, it will have 120 FPE at the muzzle, and about 90 FPE at 100 yards.... just about exactly duplicating the power of a .22LR....
Bob
Hello bob ;D
I calculated the BC of 243 - 60 Grain FN "Bowman" with the chairgun calculator and the result is 0.38 It is correct? :o
Tron
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I have not run any calcs but that sounds way high my gut says about .16 should be about right...
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I spent the day today drawing out a general arrangement of what I might build for a 6mm this winter.... Here is what I came up with so far.... I used my typical reversed tank block to keep the weight of the bottle centered.... and I may use a 1.25" OD x 0.095 wall 2024-T3 tube to keep the weight down....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/6mm%20Sporter_zpsoihmeiqp.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/6mm%20Sporter_zpsoihmeiqp.jpg.html)
I have already ordered a tank from AliExpress.... its a 500 cc Carbon Bottle rated at 300 bar.... the plan is to have an adjustable regulator built into the tank block, feeding a 150 cc plenum at about 200 bar.... I would like to use 3mm thick carbon fibre sleeve on the 14mm OD barrel, so the OD will be 20mm (over 3/4").... which should make it VERY stiff.... The plan is to use a PRod trigger group and an AR style stock in line with the main tube.... That will put the adjuster for the SSG inside the buffer tube.... A Cothran valve will handle the air delivery, with it's 0.257"ports perfect for the job.... If I can arrange it, I will get two 10" twist barrels, one in 6mm and the other in .257 cal., both 28" long.... The goal is to drive my 2.5 cal long BBTs at 950 fps, meaning about 130 FPE in 6mm and 156 FPE in .257....
I would think the BC of the 60 gr. Bowman would be slightly less than the SD, I would seriously doubt the FF is less than 1.0.... My guess for the BC is about 0.14....
Bob
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Wow nice idea bob
I want build a rifle like a Brocock bantam or bottled bullpup, but in a caliber that allows me to reach about 80 FPE, with a BC greater than 0.1 but having a large number of shots.
I was looking at the combination .25 caliber, shooting the 51 gr BTT @ 850 FPS
I´m limited in the materials here in Chile, I can only get 0.25 barrels with 1:17 twist. I don´t know if will be sufficient to stabilize the 51gr BBT
The use for this gun will be rabbit hunt (long shoots about 100 yards) What do you recommend?
(sorry for my bad english :-[ )
Tron
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Bob, I would be interested if I had the knowledge and talent to build that rifle. That looks and sounds like something I would buy for coyotes.
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Mauricio.... I doubt if the 17.7" twist LW would handle the 51 gr. BBT....
Rich.... sorry, I don't build for others.... not enough time for my own projects....
Bob
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Mauricio.... I doubt if the 17.7" twist LW would handle the 51 gr. BBT....
ops :-\ , the king heavy mkII can work in 17.7 twist?
I can buy barrels from arrowy flier (China) , but i dont know if I a can buy barrels in USA maybe I could have problems in customs.
bob you have a CAD drawing of your future build? if it is you can send me the CAD? please :-[ msuazoc@gmail.com
I pretend to use it as a guide for my future constructions :D
Tron
(http://iforce.co.nz/i/1ed3k2rs.mv0.jpg)
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Mauricio.... The 34 gr. King Heavy works well in the 17.7" twist of an LW or Hatsan barrel, I can drive them at 960 fps.... Interesting all the twist rates in that ad from Taiwan are the same as LW.... same caliber offerings, too.... I am a long ways away from a finished drawing, it is really just a general arrangement at the moment.... In fact, I seldom do complete drawings, I just use my 2D drafting program to make sure everything will have enough room to fit, and then go straight to making the parts....
Bob
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Mauricio, could you share the link for that page that's in English?
Thanks.
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Mauricio, could you share the link for that page that's in English?
Thanks.
Hello rich
the page does not exist in english, This information was sent me by Cally, the sales agent
she sends me two images, in one the price of the barrels, in the other the information of twist grove land etc
(http://iforce.co.nz/i/ujinsaut.map.png)
Tron
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Mauricio.... I doubt if the 17.7" twist LW would handle the 51 gr. BBT....
Hi Bob... what would be the best twist for the 51 BBT to achieve 950 fps?
Regards
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The 51 gr. BBT in .25 cal was designed for a 16" twist.... It may work in a 17.7" twist if you don't push it too fast.... How fast is "too fast" I can't tell you, sorry....
Bob
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Mauricio.... I doubt if the 17.7" twist LW would handle the 51 gr. BBT....
Hi Bob... what would be the best twist for the 51 BBT to achieve 950 fps?
Regards
I use the bergerbullets twist rate calculator and I got as a result this:
(http://iforce.co.nz/i/nggdghra.nl4.png)
I do not know if this calculator will be confiable
Tron
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I do not see any allowance on the Berger calculator to input the boattail dimensions.... Boattails require a faster twist....
http://www.geoffrey-kolbe.com/barrel_twist.htm (http://www.geoffrey-kolbe.com/barrel_twist.htm)
Bob
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I do not see any allowance on the Berger calculator to input the boattail dimensions.... Boattails require a faster twist....
http://www.geoffrey-kolbe.com/barrel_twist.htm (http://www.geoffrey-kolbe.com/barrel_twist.htm)
Bob
Thanks for the twist calculator bob :D
Tron
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I wonder, if the 6mm would work well in a modified Mrod?
CF tank
WAR bottle adapter
Cothran Powerhouse valve
Thoughts?
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I rather doubt you can get the FPE you need without using a Cothran valve, which is my plan.... There would not be much use in regulating it for a 6mm, so you would be limited to a few shots, and the declining velocity that occurs with that valve.... I don't know enough about the Cobra valve to comment if it could be used unregulated at over 100 FPE....
Bob
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I rather doubt you can get the FPE you need without using a Cothran valve, which is my plan.... There would not be much use in regulating it for a 6mm, so you would be limited to a few shots, and the declining velocity that occurs with that valve.... I don't know enough about the Cobra valve to comment if it could be used unregulated at over 100 FPE....
Bob
I'm confused- Bob, who are you responding to?
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Tom, I should have read the rest of your post.... I just read the first line, so my response was based on "modified MRod", thinking of starting with the regular tube and a 3000 psi fill.... Me bad!.... Yes, what you describe is basically what I am going to build, except the bottle will be reversed.... Regulated at 2900 psi is the plan, which is the pressure I tether at as well....
Sorry for the confusion.... :-[
Bob
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Bob...How many shots do you expect to have with that configuration?
Tron
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Tom, I should have read the rest of your post.... I just read the first line, so my response was based on "modified MRod", thinking of starting with the regular tube and a 3000 psi fill.... Me bad!.... Yes, what you describe is basically what I am going to build, except the bottle will be reversed.... Regulated at 2900 psi is the plan, which is the pressure I tether at as well....
Sorry for the confusion.... :-[
Bob
Ah! No worries Bob! Excellent! I really wish I could like the reverse bottle configuration, but I just can't. Do you think a bottle in the "normal" configuration will perform nearly as well?
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Tron.... hadn''t really given it much consideration.... but assuming a 4350 psi fill and 2900 psi setpoint on the 500 cc bottle, that gives me 100 bar x 30.5 CI = 3050 CI of air available.... If I can get 120 FPE (60 gr. @ 950 fps), that works out to about 25 shots at only 1.00 FPE/CI.... so that would be a rough guess / nice goal....
Tom.... There should be no difference in performance with a different bottle location.... Since there is a regulator in between the bottle and plenum, the air in the plenum is what will be doing all the work.... If I use the reverse tank, the plenum ends up being long enough to be about 150 cc, which is plenty, even for a stout .257 cal (which I plan for an optional barrel).... If you put the bottle in front of the plenum, then you are unlikely to have such a long tube.... The tubes I got from Travis which I based my BRods on works out to about 80 cc including the valve.... That's big enough for a 120-160 FPE gun, but you will have to increase the setpoint about 100-200 psi to compenstate for the smaller air on deck available to make the shot.... That will ultimately cost you on shot count, compared to having a larger plenum....
Bob
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I'm a bit confused about this regulator you keep speaking of Bob- I thought the bottle threaded directly to the WAR adapter? Or does it use a tank w/a ninja reg?
EDIT: Okay, I should have read your posts better Bob- I see you're planning to use a reg in the tank block... So there's that.
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If you are using Travis' tank current tank block (FLEX) you can either use a regulated tank, OR he can supply you with a threaded adapter so that you mount the tank directly to the block (unregulated).... His new tank block for the COBRA has an adjustable regulator built into it (great with the Cothran valve), and you just mount the tank using the adapter.... My reversed block will have a regulator inside it, like Travis COBRA block (I hope).... if not, I will use a slightly longer tube and a regulator on the bottle.... You can get regs. with 18m x 1.5mm threads that are 4500 psi input, and set the output to around 3000 psi with shims (and maybe stiffer Bellevilles)....
Bob
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Ah, cool beans- I'm using the non-COBRA block. Thanks again Bob!!
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Bob,
These may be silly questions, but how do you determine projectile nose length and meplat diameter?
Thanks
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I worked with Robert McCoy's "McDrag" program to come up with some basic designs, and then refined the relationship between the Ogive radius and Meplat diameter using that, and found that the drag seemed to go through a minimum around Mach 0.9 when the angle where they met was about 20 degrees.... Using that, I came up with a series of bullets of different length/diameter ratios from 1.25 to 4.0 where the Meplat got smaller as the Ogive got longer (to stay close to that 20 deg).... Once I had that series of designs I simply scaled them up and down for the various calibers.... The SD changes from caliber to caliber of course, because of the square/cube rule.... but that is how I got my basic proportions....
If you were working with flat base design, you could use a longer nose (and a smaller Meplat) for the same overall length, of course.... but the boattail reduces the drag more than the longer nose does.... It's all a compromise, and one of the problems with a boattail is that it needs a faster twist for the same overall length to stabilize it.... What the boattail does is give you a lower Form Factor, so that you get a better BC for a given SD (weight).... Boattails are actually more effective Subsonic than they are Supersonic.... something which I think have been largely overlooked, with a few exceptions, like the Lapua Subsonic bullet for the .300 Blackout (Whisper).... I am trying to bring that technology to airguns with my BBTs....
HTHs....
Bob
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H&N & JSB needs to make pellets to fit standard firearm bore barrels' 6 mm is
A super acurrate cal. Thats why they win so many bench rest competitions'
The triple deuce was the king then the 6 mm ppc dethroned it then came the
6 mm rem br, 6 mm tall dog' 243win' 6mm rem' 243Ack' 6 mm ack' 240 Gibbs' ect
6 mm is a natural & needs to be in the airgun world'
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Thanks for the detailed info, Bob.
Is this the Lapua bullet?
Even if its not, how would its BC compare when fired backwards at 900 FPS, compared to point first? I presume it would actually be more stable flying base first, as bullets flip over when they meet denser than air substances like ballistic gel (assuming they don't mushroom).
(http://media.midwayusa.com/productimages/large/381/381996.jpg)
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Thanks for the detailed info, Bob.
Is this the Lapua bullet?
(http://media.midwayusa.com/productimages/large/381/381996.jpg)
Naw diss be the one
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Naw diss be the one
That does not look like a .300 Blackout...
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H&N & JSB needs to make pellets to fit standard firearm bore barrels' 6 mm is
A super acurrate cal. Thats why they win so many bench rest competitions'
The triple deuce was the king then the 6 mm ppc dethroned it then came the
6 mm rem br, 6 mm tall dog' 243win' 6mm rem' 243Ack' 6 mm ack' 240 Gibbs' ect
6 mm is a natural & needs to be in the airgun world'
[/
They are not accurate just because they are 6mm bullets, other than a higher B.C. The 6PPC and 6BR have a higher velocity and do better in the wind. That and when shot for score, make a bigger hole. The .30BR is rapidly gaining ground in score competition.
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subscriber.... Yes, that is the 200 gr. Lapua bullet for the Blackout.... Here is the BBT I call the Whiteout....
(http://i378.photobucket.com/albums/oo221/rsterne/Bullet%20Casting/308%20BBT%20Whiteout2_zpskdg5cqi8.jpg) (http://s378.photobucket.com/user/rsterne/media/Bullet%20Casting/308%20BBT%20Whiteout2_zpskdg5cqi8.jpg.html)
And a .257 cal copy of it which weighs 113 gr....
(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/NOE%20257%20cal%20113%20gr_zpsepq1ol4r.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/NOE%20257%20cal%20113%20gr_zpsepq1ol4r.jpg.html)
While the two bullets are virtually identical in design, the Sectional Density of the .308 cal is higher because of the square/cube rule.... That difference in SD means that while the .257 cal reach 1000 fps on air, the .308 cal needed Helium.... However, using 4500 psi of Helium, it duplicated the ballistics of the .300 Blackout/Whisper....
I would agree that there is no "magic" in the 6mm caliber, nor in any caliber.... The downside to using larger calibers in benchrest is the added recoil.... but they have the advantage that for the same bullet shape (FF) they have a higher SD and hence BC.... That gives them the advantage in wind.... Smaller calibers in airguns use less air, and as I explained in my first post in this thread, the .224 cal would be great if you could get barrels and bullets that were compatible for our use.... The reason I want to try the 6mm is that such a combination already exists (at least in theory).... with barrels available at reasonable cost (which for me is always an issue)....
Bob
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Here is the BBT I call the Whiteout....
Thanks Bob,
What happens to the BC if you shot your bullets backwards?
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No idea....
Bob
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Bob, I am no knocking the 6MM just pointing out why the 6 PPC took over PB benchrest. In my warped mind, I think you need to find the balance between weight and BC, and I have not a clue where the magic spot is. I am guessing it is closer to .25 or 6.5mm. That Laupua bullet has been around a long time, and other than them has really never caught on, so I have to wonder why.
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Huge difference between a PB with 40-50Ksi chamber pressure and an airgun with 3-4 Ksi.... No question, finding he correct SD (weight for a given caliber) is important, and in airguns that is mostly related to pressure and barrel length.... Basically the higher the SD, the higher the BC as well.... but it is more difficult to accelerate it to useful velocities....
Bob
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I ordered a couple of 1M pieces of Carbon Fibre tubing from China through eBay.... Excellent service, less than 2 weeks to receive them.... I can't believe how stiff this tubing is....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/14%20mm%20x%2020%20mm_zpshccqe0dp.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/14%20mm%20x%2020%20mm_zpshccqe0dp.jpg.html)
It is 20mm OD and 14mm ID, so that means the wall thickness is nearly 1/8".... It is about the same stiffness as steel tubing at a fraction of the weight, and will make the barrel incredibly stiff.... I was talking to Mike at TJ's, and he thinks he can hammer the barrel down to 14mm to fit inside the tubing, I am sending him the 6" long piece in the photo as a sample....
Bob
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Oooh man!! If Mike can get his blanks to fit this tubing with little to no work on our end, I'm all in- I'm going to attempt to assemble/tune a Brod for the Bowman 6mm cast boolit...
Bob, would you have a link, or search criteria for that CF tubing?
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2 pieces, 1000mm long.... http://www.ebay.ca/itm/2pcs-20mm-ODx-14mm-IDX-1000MM-1m-Long-carbon-Fiber-tube-3k-Tubing-pi-pe-F-20-14/132123517988?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2055119.m1438.l2649 (http://www.ebay.ca/itm/2pcs-20mm-ODx-14mm-IDX-1000MM-1m-Long-carbon-Fiber-tube-3k-Tubing-pi-pe-F-20-14/132123517988?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2055119.m1438.l2649)
1 piece.... http://www.ebay.ca/itm/20MM-OD-x-14MM-ID-X-1000-MM-1m-Long-carbon-Fiber-tube-3k-Roll-Wrapped-20-14-/142186983307?hash=item211b012f8b:g:M1kAAOxy7nNTWhsV (http://www.ebay.ca/itm/20MM-OD-x-14MM-ID-X-1000-MM-1m-Long-carbon-Fiber-tube-3k-Roll-Wrapped-20-14-/142186983307?hash=item211b012f8b:g:M1kAAOxy7nNTWhsV)
Mike's 6mm blanks are normally 9/16" OD, but he thinks he can just hammer-forge it smaller to fit inside the 14mm CF tube.... I guess we'll find out!....
Bob
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You could have him OD grind the barrel also. He told me once it was like $18.
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1 piece.... http://www.ebay.ca/itm/20MM-OD-x-14MM-ID-X-1000-MM-1m-Long-carbon-Fiber-tube-3k-Roll-Wrapped-20-14-/142186983307?hash=item211b012f8b:g:M1kAAOxy7nNTWhsV (http://www.ebay.ca/itm/20MM-OD-x-14MM-ID-X-1000-MM-1m-Long-carbon-Fiber-tube-3k-Roll-Wrapped-20-14-/142186983307?hash=item211b012f8b:g:M1kAAOxy7nNTWhsV)
Bob
Excellent! Thank you for the link Bob- I'll order a piece as soon as I am able. It'll probably be winter before I'll have this rifle together and tested...
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Doug, I asked Mike about that, and he sends them out to have it done.... I didn't get a price because he thinks he can simply reduce the OD during the hammer forging process.... I guess he gets them to the listed outside diameters now by hammering them until he gets what he wants.... He would just go a bit further to reduce from 0.562" to 0.549".... but it would have to be done at the time of manufacture.... He is making me a .257 cal 10" twist like that (14 mm OD) as well....
Bob
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Bob, Veeeeeery interesting project.
I hope that so fast twist rate will not deform pure lead bullets.
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skorec, I am using a 7" twist in my .257 Monocoque with no problems.... The "gentle shove" an airgun uses to accelerate the bullet compared to a PB (because of much lower pressures) may be the key to that....
Bob
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Bob OK. I whish you big success.
You know that that my ambition is similar ( long pellets/bullets whit PCP gun ) but at smaller caliber .177 or better any new caliber .130 with energy 12 ľFPE.
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Peter.... Check out this 27 gr. bullet in .172 cal.... http://noebulletmolds.com/NV/index.php?cPath=102_440 (http://noebulletmolds.com/NV/index.php?cPath=102_440) .... You will need about an 8" twist to stabilize it.... 2600 psi in a 24" barrel should push it into the 900s.... LW have a barrel with a 9" twist, that might work if you don't push it too fast....
Bob
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Thanks Bob,
I am awaiting for FX smooth X barrel.
http://www.airgunnation.com/topic/fx-reveals-the-new-smooth-twist-x-barrel-system/page/8/ (http://www.airgunnation.com/topic/fx-reveals-the-new-smooth-twist-x-barrel-system/page/8/)
I hope that it will able to buy only FX liner itself suitable for .177 JSB Beast pellets.
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Bob
What benefit does it have carbon fiber jacket in the barrel?
Tron
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What benefit does it have carbon fiber jacket in the barrel?
Can stabilize the inner barrel by using the carbon fiber sleeve to "stretch" the steel barrel slightly. Would stiffen it up like a "fat" steel barrel, without adding so much weight.
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Pretty much what above said- we use the carbon fiber (CF) on the outside of the barrel, to stiffen it up.
As instructed by Bob, the trick is to have the CF extend into the breech, as to not create a fulcrum- potentially making the barrel even more whippy.
For my 6mm build, as suggested by Bob, my CF sleeve will extend into the breech by 1.25".
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Carbon Fibre is stiffer than steel and many times lighter.... Even when laminated with Epoxy into a CF tube, the stiffness of the least expensive CF approaches steel, and is much stiffer than aluminum.... There are high-modulas carbon fibres (more expensive) available that are significant stiffer than steel, meaning that a CF tube of a given diameter can be stiffer than a steel barrel the same size.... The commonly available CF tubes are nearly as stiff as the same OD steel barrel, but a fraction of the weight....
If weight is not an issue (or even a benefit, as in a benchrest rifle), then using a solid steel barrel of large diameter is preferred.... I keeping the weight down is an issue, then sleeving a steel liner that is realistically too thin for the length to have adequate stiffness by gluing a CF tube over it is a great solution.... Generally, stiffer barrels have greater accuracy potential.... IMO, to provide adequate stiffness, a small caliber barrel should not be longer than about 40 times it's OD, and a large caliber should be even larger in OD.... Certainly once the length of a barrel reaches 50 times it's OD, it starts getting pretty flexible, and can definitely benefit from sleeving.... For best accuracy, even 40 times the OD is probably too great a length/diameter ratio....
Bob
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OK, so now I'm on a quest.... If you look back at Reply #17 on the first page, you will see that the plan is to use an AR style stock.... I know from nothing about them, other than that there are two styles of buffer tubes (Military and Commercial) and the buttstock needs to be the right one for the buffer tube used.... I will be purchasing a 1-3/16" x 16 UN tap to thread my adapter, so I can use either buffer tube.... I would like a stock that has an adjustable height cheekpiece, if I can find one that won't break the bank.... I will need a buffer tube and buttstock to fit it.... and I'm on a very tight budget.... as in I've sold several guns to finance this project already, and I'm quickly ending up where I will have to subsidize the build with new money, which is hard to come by....
I am open to any and all advice on a suitable buffer tube and adjustable LoP stock, preferably with an adjustable cheekpiece.... Let's start with what are the least expensive ones that will do the job, and where I can get them?.... HELP !?!?!
Bob
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Now, that's a hard one Bob- An affordable, adjustable AR stock... The only two adjustable stocks that immediately pop into my head are the Magpul PRS and the Luth-AR stocks. Both are expensive, Luth-AR being the least expensive of the two. On average, the Luth-AR stock (for an A2 length tube) is around $140. Which is about $100+ cheaper than the PRS. Luth-AR does make a version for the carbine tube, but its $20 more than the A2 version.
On my 300 blackout build, I one use of Magpul's carbine stocks (for adjustable LOP) with a cheek riser. But that isn't what you're looking for, as the cheek risers are not adjustable- you adjust cheek height via different height cheek pieces.
Just puttering about on the web, there's a new to me stock that's right at $100, from AB Arms. Not sure if they ship to Canada though:
https://www.abarms.com/A-B-Arms-Urban-Sniper-Stock-USS-p/abauss.htm (https://www.abarms.com/A-B-Arms-Urban-Sniper-Stock-USS-p/abauss.htm)
So far, that's the cheapest "real" adjustable stock I've seen. The cool part is, you use a carbine tube, and you can do the big adjustment for LOP using the carbine tube's indents, and then "fine tune" the LOP using the stock's adjustments... I kind of like the idea- an adjustable "solid" stock...
Now, looking at airsoft options, here's a clone of a Mako stock:
http://www.dhgate.com/product/2016-new-arrival-special-offer-stocks-black/391942204.html#s1-18-1b;srp|1023849275 (http://www.dhgate.com/product/2016-new-arrival-special-offer-stocks-black/391942204.html#s1-18-1b;srp|1023849275)
I'm just not sure of the quality of the plastic- though, since your application is for an airgun, and not a tactical rifle you're going to be beating on, I think this would be a good choice, and cost effective...
Here's another one, a clone of what looks like a CAA stock- much more expensive than the clone Mako stock, but it comes with a monopod and (to me) looks better:
http://www.dhgate.com/product/2016new-ipsc-glock-gun-command-caa-ars-multi/387880774.html#s1-22-1b;srp|1023849275 (http://www.dhgate.com/product/2016new-ipsc-glock-gun-command-caa-ars-multi/387880774.html#s1-22-1b;srp|1023849275)
Just some food for thought.
---EDIT---
ADDITIONAL INFO:
Here's another stock I found, but I don't know if they ship to Canada:
https://www.cheaperthandirt.com/product/imi-enhanced-m4-stock-with-polymer-cheek-rest-imi-zs200-813782025402.do?sortby=ourPicksAscend&page=2&refType=&from=fn (https://www.cheaperthandirt.com/product/imi-enhanced-m4-stock-with-polymer-cheek-rest-imi-zs200-813782025402.do?sortby=ourPicksAscend&page=2&refType=&from=fn)
EDIT: Okay, the Cheaper than Dirt stock won't ship to Canada- but what I can do is buy it, and ship it to you... I don't think ITAR's covers stocks, does it? PM me if interested in going this route Bob- $50 for an adjustable LOP and adjustable cheek AR stock isn't too shabby!!
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Actually, I think the DHGate stock would be fine for my purposes.... I will also need a buffer tube to mount it on (and lock nut?).... Any idea which one, maybe I can get them both from DHGate?.... They do ship to Canada.... Is this the correct buffer tube?....
http://www.dhgate.com/product/223-5-56-model-4-15-mount-carbine-buffer/391941326.html#minicart-1-null (http://www.dhgate.com/product/223-5-56-model-4-15-mount-carbine-buffer/391941326.html#minicart-1-null)
Bob
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Actually, I think the DHGate stock would be fine for my purposes.... I will also need a buffer tube to mount it on (and lock nut?).... Any idea which one, maybe I can get them both from DHGate?.... They do ship to Canada....
Bob
Excellent! I'm glad the DHGate company ships to Canada- one problem solved!
As far as which tube to use, I'm emailing the sellers now, as I'm also interested in one of these stocks- so I'll let you know!
That kit should work just fine- as all these parts are being sold as airsoft parts. You won't need the buffer and spring but it's an all-inclusive kit, so you don't really have any say in that. I haven't found individual parts yet, not even sure if they offer them...
So, if using a Mako clone, and getting that buffer tube kit, that's $52 USD rounding up... not sure how much that would be in CAD... Either way, not too shabby for an adjustable AR stock!
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Thanks, Tom, I ordered that stock and buffer tube, and a short BiPod to replace the one I just gave my son on his Hatsan.... The total (with free shipping) was $91.91 Canadian....
Bob
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Thanks, Tom, I ordered that stock and buffer tube, and a short BiPod to replace the one I just gave my son on his Hatsan.... The total (with free shipping) was $91.91 Canadian....
Bob
Most excellent! Please let me know fit and function once they come in...
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I ordered my barrels today from TJ's.... I'm getting a 6mm and a .257, both in 10" twist, that are 29" long and hammer forged to fit inside my 14mm ID CF tubing sleeves....
Bob
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Gathering the parts has so far been quite easy... I can't wait to get this build underway!!
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Tom, did you go with the 20 mm OD CF tube, or the 18mm OD ?.... Mike emailed me today, he has the sample tube I sent, has measured it, and plans to do the barrels this week....
Bob
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I'm going to go with the 18mm- I was just about to order it now, but wanted to check out what-all was going on here first... I just think 20mm will either be too large, or too close for comfort for me, as far as wall thickness of the breech... 18mm looks like it'll have more meat around the barrel, which I'm much more comfortable with. Of course, I'm just spitballing with a set of digital calipers and my eyeballs... ;D ;D ;D
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Apologies if this was already mentioned. 20 mm OD by 18 mm ID carbon fiber tube on amazon:
https://www.amazon.com/ARRIS-Wrapped-Carbon-Glossy-Surface/dp/B00RX6QTHC/ref=cm_cr_arp_d_product_top?ie=UTF8 (https://www.amazon.com/ARRIS-Wrapped-Carbon-Glossy-Surface/dp/B00RX6QTHC/ref=cm_cr_arp_d_product_top?ie=UTF8)
By the way, how does one cut this material?
-
Cut it with a hacksaw or bandsaw, then you can sand the end to get rid of any slivers....
Bob
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Thanks Bob,
How important is wet sanding and cutting to avoid releasing airborne fibers?
-
I suppose it's a good idea, but I never bother.... A dust mask would be a good idea.... I think that would look after the amount you release with a couple of cuts and sanding the ends....
Bob
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Inventory run on NOE's forum one missing from 5 signed...Any interested on this bullet here?
http://noebulletmolds.com/smf/index.php/topic,2146.0.html (http://noebulletmolds.com/smf/index.php/topic,2146.0.html)
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Well, I received my barrel from TJ yesterday, my mold is on order- a 4 cavity "Bowman" 60 grain from Arsenal. I'm still waiting on my CF from fleabay, and I'll send off my breech as soon as I get my CF. This rifle is becoming more and more of a reality!!!
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I got my barrels today from TJs.... Mike did a fantastic job of hammer-forging them to fit the sample piece of 14 mm ID Carbon Fibre Tubing I sent him.... Both the 6mm and .257 barrels I ordered are a perfect slide fit inside the CF sleeve.... They are both a 10" twist, and the blanks are 29" long....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/14mm%20OD%20Barrels_zpsgulggcha.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/14mm%20OD%20Barrels_zpsgulggcha.jpg.html)
I am slowly collecting the parts I need for this winter's projects, this was a big step along that path....
Bob
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I got my barrels today from TJs.... Mike did a fantastic job of hammer-forging them to fit the sample piece of 14 mm ID Carbon Fibre Tubing I sent him.... Both the 6mm and .257 barrels I ordered are a perfect slide fit inside the CF sleeve.... They are both a 10" twist, and the blanks are 29" long....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/14mm%20OD%20Barrels_zpsgulggcha.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/14mm%20OD%20Barrels_zpsgulggcha.jpg.html)
I am slowly collecting the parts I need for this winter's projects, this was a big step along that path....
Bob
Thank you again for letting me know you were having some barrels done up Bob- My barrel also came out about darn perfect! It slid easily into the CF tube I ordered (via link you provided), with no play. This is going to be a fun build!!
Only "bad" part is, I can't use a CF tank- I went ahead and ordered the Ninja 4.5k psi in/3k psi out reg. I could only find an Aluminium tank that would fit the reg's threads (I'm assuming 5/8-18 UNF) on Aliexpress- it's also only 450cc instead of 500 cc... But, it is a 4500 psi tank. 60mm in diameter. So about the same size as a "standard" airgun buddy bottle. Which means I can get a bipod mount for it.
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It's great news that Mike at TJ's can make .22 to .30 cal (maybe even .357) barrels in 14mm OD to fit the readily available CF tubing of that ID.... The only catch is that it's not a standard size for him, and he may not have it in stock.... All he does is hammer-forge the barrel smaller while it's on the Mandrel instead of stopping at 9/16", he goes a bit smaller.... CF tubing is available in 14mm ID with 1mm, 2mm, or 3mm wall thickness, depending on how stiff you need, and what will fit your receiver, and clear your air tube.... The 3mm wall (20 mm OD) tubing I bought is like a rock.... sooooooooooo stiff.... ::)
My 29" long 6mm CrMoly barrel weighs 1 lb. 10 oz., and with the 6 oz. CF sleeve weighs 2 lbs. even.... If the barrel was the same OD and all steel, it would weigh 3 lbs. 10 oz.... By using the 20mm sleeve on the 14mm CrMoly liner I have saved 45% of the barrel weight, with the same stiffness.... The sleeved barrel is over 4 times as stiff as the 14mm OD liner by itself, for only a 23% increase in weight.... Just 6 oz. of Carbon Fibre does the same thing as adding 2 lbs. more steel.... :o
Bob
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It's great news that Mike at TJ's can make .22 to .30 cal (maybe even .357) barrels in 14mm OD to fit the readily available CF tubing of that ID.... The only catch is that it's not a standard size for him, and he may not have it in stock.... All he does is hammer-forge the barrel smaller while it's on the Mandrel instead of stopping at 9/16", he goes a bit smaller.... CF tubing is available in 14mm ID with 1mm, 2mm, or 3mm wall thickness, depending on how stiff you need, and what will fit your receiver, and clear your air tube.... The 3mm wall (20 mm OD) tubing I bought is like a rock.... sooooooooooo stiff.... ::)
My 29" long 6mm CrMoly barrel weighs 1 lb. 10 oz., and with the 6 oz. CF sleeve weighs 2 lbs. even.... If the barrel was the same OD and all steel, it would weigh 3 lbs. 10 oz.... By using the 20mm sleeve on the 14mm CrMoly liner I have saved 45% of the barrel weight, with the same stiffness.... The sleeved barrel is over 4 times as stiff as the 14mm OD liner by itself, for only a 23% increase in weight.... Just 6 oz. of Carbon Fibre does the same thing as adding 2 lbs. more steel.... :o
Bob
That's crazy to think about!!
It is awesome that Mike can offer the 14mm OD- Going with the 18mm OD opens a lot of opportunity for the Brod crowd, as the 18mm is perfect for a factory breech... Not too big, not too small- juuuuuust right!
I too am slowly gathering parts for this build.
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The 18mm OD CF sleeve would only add about 4 oz. of weight (15%), and it would nearly triple the stiffness of the 14mm barrel by itself....
Bob
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Just curious, why bother with 6mm/.243 when .25 is already so popular? Why not just make the bullets in .25 cal.?
Don't get me wrong, my only centerfire rifle is a 6mm Remington. I think it's a great caliber. But for airguns, where we're shooting much shorter distances? I dunno, it just doesn't seem like we need that many calibers.
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Depends which is shorter distances? Here in Finland we shoot @ 300m soda cans 12oz for fun...Thats basicly longest shooting range where we could go shooting here.
There is topic where Carl shoots 1100 Yards at .257...And soda cans at 800 yards IIRC.
And my opinion is fun to try find "new" calibers which could perform well 100m 200m 300m or longer or any distance.
And good bench rest airgun is also nice to get.... And at this forum is guy who shoot .25 Taipan at 250 yards on golfball... that is long distance for diabolo...can't remember who it was but that topic is here with video.
And there is .25 bullets available on NOE's forum. Few desings by Bob and few basicly desingned for .25 acp...
http://noebulletmolds.com/smf/index.php/topic,1897.0.html (http://noebulletmolds.com/smf/index.php/topic,1897.0.html) and http://noebulletmolds.com/NV/index.php?cPath=374_376 (http://noebulletmolds.com/NV/index.php?cPath=374_376)
I've been looking long .25 blank barrel haven't find any suitable yet...
Testing new is part of this hobby and it is interested.
Edit: that user is Bizill and topic is here
https://www.gatewaytoairguns.org/GTA/index.php?topic=130647.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=130647.0)
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Just curious, why bother with 6mm/.243 when .25 is already so popular? Why not just make the bullets in .25 cal.?
Don't get me wrong, my only centerfire rifle is a 6mm Remington. I think it's a great caliber. But for airguns, where we're shooting much shorter distances? I dunno, it just doesn't seem like we need that many calibers.
Page 1, reply 4... Not being snarky, just wanted to reference that post, in case you didn't want to read through the entire thread.
No real reason for me- just want to be different. I'm also still waiting on a .257, and figured this would be a good, relatively simple project that doesn't require too much work on my part. At it's core, my bottle conversion Marauder is just a jumble of modified factory parts and aftermarket parts fabercobbled together to form a cohesive airgun. I've been wanting to do up a Brod build for a while, but didn't want to do .30, .25 or .257 because I already have one or more in each of those calibers. I didn't want to do a .357 because that's not a simple build for me, for what I want it to do, and I also am not ready to flat out purchase an airgun for a sum that's greater than what I spent building my Reminton Model 7 in .300 BLK... Which wasn't too much, considering: well under $1k assembled from parts, aluminium chassis with scope and rings.
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For me it is two things first is in the long run I would like to see PCPs available in as many calibers as there are in the other disciplines...
But for me well .243/.244 is a great fit for a near stock Mrod... 1 in 12 to 1 in 14 twist using 25g to 40g (Lighter if they started making pellets or Nick started swaging them)...
would not take a really long barrel to get to 60-70 fpe... at that power level 30g-45g cast would work well with good to decent trajectory and given the same design the 243 would have a bit higher sd and slightly better B.C. ...
Not there yet with barrels, pellets, and cast... can only hope and demonstrate for now...
In the end having more calibers is about how each can fit into more niches more closely...
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We can never have enough calibers.... but we always seem to have more than we really need.... A lot of it boils down to availability of bullets and barrels.... and what fits the job you have to do.... I'm not the first to suggest 6mm, Jack Bowman at Scandalous Airguns makes them, and through Arsenal has a 60 gr. bullet available, I have a mold currently at Erik's being hollowpointed.... While I was at it, I had Jared tool up for a 47 gr. in .224 cal which should work in the 14" twist TJ's liner.... so that makes another choice for a similar job....
Realistically, there is not much difference between any of the three calibers.... At 950 fps, with the three versions now available of the venerable Lyman 257420 through Arsenal.... you can choose....
47 gr. in .224 cal.... 94 FPE
60 gr. in 6mm/.243 cal.... 120 FPE
70 gr. in .257 cal.... 140 FPE
The larger the caliber, the more air you will use, and the more report you will get.... but you will put more energy downrange.... I don't think a Ground Squirrel on the receiving end will know what hit him with any of those.... but by the time you get up to something the size of a Coyote, there would likely be a difference in terminal performance....
Bob
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Here is the stock I ordered from DHGate, along with the buffer tube (Mil-Spec).... The fit is perfect, with about 3" adjustment in the LoP, and almost an inch of vertical adjustment for the comb height....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Stock_zpsfpojoucv.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Stock_zpsfpojoucv.jpg.html)
The stock / buffer tube assembly weighs just 1 lb. 5 oz.... and should look great with the PRod trigger group I plan on using on this build....
Bob
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We can never have enough calibers....
Bob
I agree absolutely.
Personally I aspire for caliber .13 at 12FPE
Triple the stiffness of the 14mm barrel by verry light CF tube is intersetng too.
The qustion only is why they aro not pruducing hole barrel from CF.
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I would think that wear would be the problem.... The CF tubing is carbon fibres in an Epoxy matrix, which is basically plastic.... It wouldn't take long to wear the rifling away....
Bob
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Bob, that stock looks excellent! I'm glad you're happy with your purchase!
My Ninja 4500 psi in 3k psi out reg should be here any time, and my aluminum tank should be here... soonish? I've also just received my trigger and bolt from Crosman. Mrod Gen2 main tubes are backordered. Not sure when I'll get that. I ordred mine on the 15th of August. I've also received my scope for the 6mm build- a BSA 4-14x44 with a 30mm tube. Midway has them for a whisker under $140 US:
https://www.midwayusa.com/product/456482/bsa-tactical-mil-mil-rifle-scope-30mm-tube-4-14x-44mm-side-focus-1-10-mil-adjustments-first-focal-mrad-reticle-matte (https://www.midwayusa.com/product/456482/bsa-tactical-mil-mil-rifle-scope-30mm-tube-4-14x-44mm-side-focus-1-10-mil-adjustments-first-focal-mrad-reticle-matte)
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Yeah, great scope, but shipping scopes out of the USA is almost impossible, Midway won't even consider it.... I got a 1 metre (39") long piece of 7075-T6 tubing from a buddy today, and the plan is to build the .257 around that, unregulated, instead of a bottle.... The tubing is 1.25" OD x 0.130" wall, which means it is good for over 5000 psi MSWP.... which means I can tether the gun at anything up to that.... Here is what I'm thinking it will look like....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/257%20Tethered%202_zps6rnaalbw.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/257%20Tethered%202_zps6rnaalbw.jpg.html)
The plan is to get another stock, but without the buffer tube.... and simply machine the OD of the main tube for the stock to slide over it.... The ID is 0.010" smaller than the normal 1.00" ID buffer tubes, so there is plenty of wall thickness left.... and NO weight for an adapter.... I am blown away by how light the tube is, even at that length, and with the thick wall.... The reservoir will be 300cc.... 8)
Yeah, I know this isn't a 6mm, but since I kept mentioning I was also going to build another .257, I though I would put this information in here anyways.... ::)
Bob
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Well...That 75 grain NOE's mold is now on Last Call.. 8) I started this project getting molds first :P Seriously need to figure that blank barrel... Wan't to buy good barrel...Bartlein, Krieger, Shilen etc. but my wallet dosen't like that idea so I probably wait some time..
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Teemu, I have asked Al if he can, in addition to making the 75 gr., also shorten the design by 0.080" (at the back), by plunging the tool to a shallower depth in the mold block.... This would give a bullet of about 64 gr.... So far, no answer.... If you are interested in both weights, perhaps post in the Group Buy thread, and send Al a PM, as I have?.... I would like both (2 separate molds)....
Bob
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Well....i have been sending couple PM's to Al ...One was July 17 and one August 9th and haven't got any answers yet. Must been busy time on NOE.... I've been ordering molds other places like MP-Molds.For .25 cal, .22 and .223 . MP-Molds has sale 25% off and free shipping wordwide. And checking castboolits forum too.
But yeah sure i'm interested but it could take while when we get enough interested signed to get that mold.There is "new" winds blowing at NOE...Most of group buys are slick sided HTC coating models which are useless in our hobby.
I'm a bit confused.... Having get answer usually in few days but have seen others complaining in other forums that they won't get answer PM nor emails either...
And go MRI at Saturday depending result I may need to go back surgery again so...Well I get more information on that at August 29th when doctor calls for results
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Good luck with the back surgery, Teemu.... hope it goes 100%....
Bob
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Thanks Bob. I hope too If surgery is needed
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So I got my China tank today- the Ninja valve fits beautifully... The gold and black contrast is nice too... Anyone know what the typical oring type/size is for 450cc-500cc tanks are? The factory Ninja tank oring isn't going to cut it methinks.
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How did you get a ninja reg in a Chinese tank? I have only seen 18-1.5mm threads on the carbon fiber tanks.
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How did you get a ninja reg in a Chinese tank? I have only seen 18-1.5mm threads on the carbon fiber tanks.
It's an aluminum tank, 450cc 4500 psi, that's threaded for 5/8-18 UNF. LITERALLY the only tank that would work with the Ninja reg, sized for a airgun. This thing is a beast too... as in HEAVY.
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I wonder if it would be possible to either have a custom made mag for these 6mm boolits? Or would an existing mag work? I'm thinking the Bowman boolits will be too long... I'm not worried a bit if I have to single load them, the magazine was kind of an idea that popped into my head.
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You might be able to have a custom mag made, without a cover plate?.... The maximum length in a .25 cal mag is 0.450", you might be able to grind that out and get to 1/2", but I've never tried.... The 6mm Bowman is 0.57" long.... The opening in the receiver for the Mag. is 0.70", so using a .25 cal single loading tray is a no-brainer....
Bob
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.25 cal single loading tray is a no-brainer....
Bob
I was sure this was the case, I just wanted to make sure- thanks again Bob!!
Any thoughts on what size O-ring would go in this tank of mine?
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Sorry, no.... The standard Ninja tanks use a # 016.... 5/8" ID to fit over the threads, 3/4" OD to fit inside the recess in the end of the tank.... However, if the regulator is undercut for a thicker O-ring, you may need a # 112 or a # 113.... Basically, use the one that after you put it over the male threads (or recess) fit just inside the groove in the end of the tank, and for thickness touch both parts before they are screwed hard up against each other.... so that the O-ring is under slight compression when installed....
Bob
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Any specific type? I'm assuming big box (if the even have those sizes) store o-rings wouldn't cut it?
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BunaN are fine, either 70D or 90D.... It's a static application, so nothing fancy is required....
Bob
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Sweet!! I'll go snag some to try out this weekend!!!
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The mould for the 74 gr. FN, available as GC or PB, and also with a Lyman HP Pin, are now in the store at NOE.... along with the shortened version I requested....
http://noebulletmolds.com/NV/index.php?cPath=25 (http://noebulletmolds.com/NV/index.php?cPath=25)
Bob
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I got all my material for this build a couple of days ago, and decided the first thing to do was to turn down the back of one of the tubes to fit the stock.... I got a piece of 1.25" OD x 0.120" wall 2024-T3 tubing from Lloyd Sikes, which I plan to use for the .257 version, as I am going to build two guns at the same time.... The 6mm will be a regulated gun, using the 500 cc 4500 psi CF tank I got earlier.... and the .257 version will be an unregulated version having a 300 ccc reservoir that can be filled to 4500 psi.... I hope to tether it at about 3800 psi.... The straight tube, unregulated .257 version will look something like this....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/257%20Tethered%202_zps6rnaalbw.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/257%20Tethered%202_zps6rnaalbw.jpg.html)
The tube is long enough, and a thick enough wall, that I was able to turn down the back 7" to 1.15" OD to fit inside an AR style stock.... It will be used directly over the tube, no separate buffer tube or threaded attachment required.... I used a steady rest on the lathe to support it (since it won't fit through my headstock) and turned down the butt end.... Here is a photo of the stock slid into place.... There is still 0.070" of wall remaining, so plenty of strength.... Note you can't do this with a 1.25" OD x 0.095" wall tube, because the remaining wall would be too thin.... so the 6mm version which uses that tube will have to have a conventional threaded adapter to hold the buffer tube assembly....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Tube%20Turned%20Down_zpshpc4yf21.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Tube%20Turned%20Down_zpshpc4yf21.jpg.html)
With the tube slid in until the back of it hits inside the back of the stock, there is a bit under 1/4" of smaller OD tube showing, and the trigger will be mounted so that the LoP can be adjusted from 12 to 16".... At a 14" LoP it will look about like in the photo.... I have to mount a piece of aluminum barstock on the bottom of the tube to prevent rotation of the stock, and provide holes for the fore-and-aft adjustment feature.... The stock can be slid right off the back for access to the preload and gap adjustment of the SSG using a socket and/or screwdriver.... I will be using Prod trigger groups on both builds, with a taller sear supplied by Lloyd, which is intended for the 0.095" tube wall.... Since this tube is thicker, I will be milling a flat on the bottom of the tube and the top of the trigger group to get the correct sear engagement....
Bob
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I really like your design. Is this single or multi shot, I cannot recall.
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Both these will be single shot.... I am considering either machining the loading tray into the barrel.... or using a spindle with an integral loading tray so that I can index the barrel.... haven't decided yet.... I like the idea of drilling the receiver straight through at a large diameter (I have some 12" long drills) instead of having a small (loading) section in the middle and having to drill from both ends.... That tends to cause misalignment between the barrel and bolt.... at least I seem to have difficulty getting the alignment perfect when I do it....
The other advantage is that I can make both receivers identical and just have different ID spindles.... or machine each barrel to suit....
Bob
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I suspect that would provide about as straight a feeding/seating as you can get. And a loading tray into the barrel, I envision something similar to how the QB barrels are machined?
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Yes, drill the chamber into the breech end of the barrel at the appropriate diameter, and then mill half the barrel away, leaving a loading tray like the QB setup.... The drawback is you may need a very long chambering reamer, it has to go from the back of the loading tray to the front of the tapered leade.... If using a spindle to index the barrel, the chamber and leade is machined into the barrel, but no port, and a lip that inserts into the spindle.... A matching recess is in the front of the spindle, housing an O-ring to seal against the barrel, and the port and a parallel chamber machined into that.... then the back half is milled away to form the loading tray.... NOTE that the spindle must be secured into the receiver as there is considerable rearward thrust acting on it, and also forward on the barrel (pressure x barrel OD^2 x PI/4).... If they are not separate pieces, the forward force on the barrel is reduced, as is the rearward thrust on the bolt face.... because the pressure only acts on the bore area (where it seals against the bolt face), not the barrel OD cross-section.... Another alternative is to make the loading tray a separate piece, so no load on it, just on the barrel and (inserted) bolt.... Lots of things to think about, strength-wise, either way....
Bob
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Yes, drill the chamber into the breech end of the barrel at the appropriate diameter, and then mill half the barrel away, leaving a loading tray like the QB setup.... The drawback is you may need a very long chambering reamer, it has to go from the back of the loading tray to the front of the tapered leade.... If using a spindle to index the barrel, the chamber and leade is machined into the barrel, but no port, and a lip that inserts into the spindle.... A matching recess is in the front of the spindle, housing an O-ring to seal against the barrel, and the port and a parallel chamber machined into that.... then the back half is milled away to form the loading tray.... NOTE that the spindle must be secured into the receiver as there is considerable rearward thrust acting on it, and also forward on the barrel (pressure x barrel OD^2 x PI/4).... If they are not separate pieces, the forward force on the barrel is reduced, as is the rearward thrust on the bolt face.... because the pressure only acts on the bore area (where it seals against the bolt face), not the barrel OD cross-section.... Another alternative is to make the loading tray a separate piece, so no load on it, just on the barrel and (inserted) bolt.... Lots of things to think about, strength-wise, either way....
Bob
This is very interesting, as it makes me consider the various configurations such as the QB, Sam Yang, amd my PBBAs with threaded barrel:receiver with no porting.
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Excellent Bob! I'm glad one of us is making progress! I'm still waiting on funds to buy the Cobra block. After that, I should be good to start modifying my breech, tube, then assembling it. There's still a few things I need to decide though- what kind of stock do I want, and whether or not I want to add an LDC... If I do add an LDC, how to go about it. The little things! ;D ;D
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Follow the air path from the port to the bullet.... that entire area is pressurized, along with the bolt face.... If there are any breaks in the surface, follow the air out to where it hits a seal such as an O-ring.... Best case is to calculate the end force based on the diameter of the O-ring.... However, if the O-ring fails (and the air has nowhere to go), you may need to use the OD of the barrel (spindle, etc.) to calculate the end force.... Let's say the end of a 16mm (~5/8") OD barrel might see pressure if an O-ring leaked.... At 3000 psi, that is 935 lb.f., so at a 3.5:1 safety margin you need to engineer the barrel retention for 3271 lb.f.... :o
By comparison, if the only seal is barrel to bolt face, and it's a .257 cal, the forces on barrel and bolt at 3000 psi are only 156 lb.f.... and 3.5 times that is "only" 544 lb.f....
Bob
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At 3000 psi, that is 935 lb.f., so at a 3.5:1 safety margin you need to engineer the barrel retention for 3271 lb.f.... :o
Bob
Yowza! I wonder what Marko's 20mm............. :o
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"Well engineered" is the answer....
Bob
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"Well engineered" is the answer....
Bob
Tru dat! ;D
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I finished the machining to mount the stock and pistol grip today.... I decided to lengthen the locking pin by 3/16" and simply drill holes in the tube for the adjustable stock positions.... The locking pin is 5/16" diameter, so all I did to lengthen it was drill and tap it 10-32 and installed a short SHCS.... The head is 3/16" thick, exactly the length I needed.... I drilled seven 5/16" holes on 5/8" centres, so I have 3.75" of adjustment for the LoP.... In order to keep the stock from rotating I milled a short block of aluminum 1/2" wide x 3/8" tall, which I attached to the back of the tube with two low-profile 6-32 SHCSs.... The block prevents the stock from pulling right off the end while adjusting it, unless you lift up on the front of the adjusting lever, the same way the stock works on an AR buffer tube....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Tube%20Machined%20for%20Stock%20and%20Grip_zpshrkmrh9q.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Tube%20Machined%20for%20Stock%20and%20Grip_zpshrkmrh9q.jpg.html)
I laid out the location of the trigger group so that my LoP is adjustable from 12" (mostly for transporting it) to 15.75".... I drilled and tapped the mounting holes in the tube for the trigger group, and milled the slot for the sear.... The photo below shows what the stock and grip look like mounted to the main tube.... set for a 14.5" LoP, which is what I use most of the time....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/257%20Stock%20and%20Grip_zpsm29bqrtl.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/257%20Stock%20and%20Grip_zpsm29bqrtl.jpg.html)
I'm very happy with the appearance, simplicity, light weight and the ergonomics, and I will set up the 6 mm bottle gun with the same dimensions....
Bob
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That's gorgeous Bob!
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Very nice! I went back to review your post on Nove 30 where you mentioned simply turning down that portion, that will provide a nice rigid shooting platform!
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The bottle gun version uses a 0.095" wall tube, which would be too thin if I turned the outside down to fit inside the AR stock.... Therefore I have to use a buffer tube to mount it, and that requires an adapter to the MRod size tube.... Here is what it looks like....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Stock%20Adapter_zpseebcxait.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Stock%20Adapter_zpseebcxait.jpg.html)
It was made from a piece of bar stock, turned down to 1-3/8" OD for 1" of length, and that portion drilled out to 1-1/8" and then tapped 1-3/16"-16 TPI to fit the buffer tube threads.... I have a maximum of 5/8" thread engagement.... The adapter was drilled through to 19/32" and then tapped to 5/8"-28 TPI for my SSG gap adjuster.... The front half was turned down to 1.058" to fit inside the MRod diameter tube a total of 0.70", and mounting holes drilled and tapped for 8-32 screws top and bottom that will be 1/2" from the end of the tube.... This puts the rear trigger mounting hole 1.50" from the back of the adapter.... and that ends up in exactly the same place as the shoulder on the turned down version I made yesterday.... When assembled (without the tube) it looks like this....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/6mm%20Stock%20Assembly_zpsg0m5e7we.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/6mm%20Stock%20Assembly_zpsg0m5e7we.jpg.html)
With the stocks adjusted in the same holes, the LoP of both guns are the same, so they will share identical ergonomics.... I still have to make an insert for the straight through tube to mount the SSG and the rear of the trigger group.... and of course the SSG assemblies, but those will come much later when I have the valves and hammers made....
Bob
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Today I made the SSG adjusters.... In this style of SSG, the center stop rod is stationary (but adjustable) and a spring guide slides on it to compress the spring and then launch the hammer when you pull the trigger.... The adjusters were made from a 2" piece of 3/4" OD CRS, machined down to 5/8" for half the length and threaded 5/8"-28 TPI to match the inside of the SSG mounts.... The inside was drilled to 1/2" ID for 1.5" deep to provide a place for a longer than normal hammer spring.... The back part of the adjuster was drilled and tapped 1/4"-28 TPI for the adjustable stop rod.... With the adjuster screwed fully in, there is 2.5" available to the back of the hammer, and with it out all the way (about 3/4" of adjustment) I have enough room for a 3" hammer spring with no preload.... I have not yet made the spring guide which slides on the 1/4" stop bolt and propels the hammer.... Since both threads are the same pitch, you can hold the stop bolt with a screwdriver (you can see the slotted end in the photo) and adjust the outer sleeve to change the preload without changing the gap.... If you hold the outer adjuster, CW on the stop rod decreases the gap (and preload) and CCW increases the gap (and preload)....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/SSG%20Parts_zpsw9mauvcg.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/SSG%20Parts_zpsw9mauvcg.jpg.html)
You can see that I have milled flats on the back of the adjuster, and I will be making a custom socket wrench to fit that.... Three sides are milled flat, 3/16" from the center, and you can make the initial adjustments with a 3/8" wrench.... One side is left unmachined, but is drilled and tapped for an 8-32 setscrew which will have small Delrin plug under it, pushing on the side of the 1/4"-28 threads as a brake.... There is a similar brake in the outer plug (the straight one for the one-piece tube is shown) to act as a brake for the 5/8"-28 threads on the adjuster.... These allow you to adjust the SSG preload and gap, but insure that the adjustments don't move on their own....
The stop rod shown was made from a 3" long bolt, and is too short to use with a 3" spring.... I will be making longer ones when I make the sliding spring guides....
Bob
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Today I made the wrench for adjusting the SSG through the end of the main tube.... The wrench consists of three parts, an extension tube, made from a leftover front piece of a Disco reservoir, a front end machined to fit onto the SSG Adjuster only one way, and a back end which mounts the handle and has a guide for the screwdriver....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/SSG%20Wrench_zpsdrtdsn9f.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/SSG%20Wrench_zpsdrtdsn9f.jpg.html)
The handle is simply a 3" long 1/4"-28 bolt, which will be locked in place with a locknut.... It is threaded into the rear mount, which is drilled 1/4" ID and turned to fit into the Disco tube.... The front end (lower left) is turned from a piece of 1" aluminum, with a 15/16" OD to fit through the back of the buffer tube, which I drilled out for that purpose.... It is also drilled through 1/4" for the screwdriver, and to allow the threaded stop rod to enter it, because it sticks out past the end of the SSG adjuster (see bottom right).... I milled a slot in the end of the wrench portion that is 3/8" wide, right out though one side, but blind on the other, where I used a 3/16" mill to create clearance in the corners.... That left a bump between which helps to center the tool on the end of the SSG adjuster.... It will only fit on one way.... The back of the wrench end is threaded 13/16"-28 to thread into the front of the Disco tube....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/SSG%20Wrench%20Parts_zps4qkmsl28.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/SSG%20Wrench%20Parts_zps4qkmsl28.jpg.html)
I used some Loctite 638 (green) to permanently install the front (wrench) end in the threads of the Disco tube, and then drilled the hole for the handle in the same plane as the slot, so that the bolt which serves as a handle points to the open end of the slot.... This corresponds to straight up in either gun, when the SSG adjuster is tightened in all the way, making it simple to count turns out from full in to determine the position of the adjuster....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/SSG%20Wrench%20Operation_zpsv6sqnhrh.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/SSG%20Wrench%20Operation_zpsv6sqnhrh.jpg.html)
A long slotted screwdriver fits through the center of the wrench to engage the slot in the end of the stop rod.... This allow you to hold the rod and turn the adjuster (adjusting preload but not gap), to hold the adjuster and turn the stop rod (increasing or decreasing both), or without using the screwdriver simply turn the adjuster which moves the rod in as well (adjusting gap but not preload).... The bolt handle just clears the back of the tubes when the adjuster is all the way in, so all you have to do is slide off the stock to adjust the SSG....
Bob
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Great Bob
I was wondering about your method of madness, leaving the slot?
Now it becomes clear. LOL 8)
Outstanding work, I like it, waiting for the next chapter>>>>>>
Tia,
Don
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This afternoon I made the spring guides and longer stop rods.... The guides were turned from Delrin rod, and are 0.35" OD x 1.5" long where they fit inside the spring and 0.59" OD on the flange, which is 1/8" thick.... They were drilled out with an "F" drill (0.257") so that they slide easily on the 1/4" rod.... There is a # 010 O-ring between the flange and the stop on the rod to act as a buffer.... The stop rods were made from a 4" long piece of 1/4" drill rod, threaded 1/4"-28 TPI for 1.5" of length to provide lots of adjustment.... The other end was also threaded 1/4"-28, and a nut bottomed in the threads, tightened down with Loctite 638 (green) to glue them permanently in place.... The nut was then turned down to 0.40" OD and contoured to the same shape as the bottom of the 7/16" drilled hole which will be drilled in the hammer.... The flange on the spring guide is what allows the hammer to compress the spring, and transmits the spring force to the hammer on firing....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Spring%20Guide%20and%20Longer%20Rod_zps8a3kpkm9.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Spring%20Guide%20and%20Longer%20Rod_zps8a3kpkm9.jpg.html)
This style of SSG has a couple of advantages.... First, it can be adjusted from the back without disassembly to change the preload like some of my earlier ones.... Secondly, other than the hammer, the only weight which is being accelerated by the spring is the very light Delrin guide, so little energy is lost.... The top assembly in the photo above is adjusted so that there is no preload on the 3" spring, and the distance between the flange on the guide and the mounting block is 1", which will be the maximum cocking distance I will build into these guns.... As you increase the preload, the slotted end of the stop rod will protrude more from the back of the SSG adjuster.... I have enough thread to allow nearly 1" of preload, which is more than I will ever use.... 3/8" preload on the 14 lb/in spring shown works out to 5 lbs.... If I run out of preload it is a simple matter to add a shim to the end of the spring inside the adjuster.... I'm very happy with how the SSG part of this project has turned out, next step is to think about the design of the hammer and make those....
Bob
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Wow. I some how missed this. Looks good so far!
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I worked on the PRod trigger groups today.... Lloyd Sikes of AirGunLab makes taller sears so that the PRod pistol grip style trigger can be used with the thicker tube of an MRod.... The sear is about 0.030" taller, to make up for the 0.095" wall compared to the 0.0.65" wall of the PRod.... Lloyd's taller sear is on the left....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Tall%20Sear_zpsdejvskyl.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Tall%20Sear_zpsdejvskyl.jpg.html)
It is made from hardened steel, and extremely well made.... On the 6mm bottle gun, which uses a 0.095" wall tube, all I needed to do was install it in place of the stock one.... The straight tube I will be using on the .257 is 0.120" thick wall, however, so even the tall sear would be too short.... Fortunately, I had a solution.... The first gun I made with a PRod trigger group on a 0.095" wall tube (my Monocoque .257) I didn't have a tall sear, so I machined the top of the trigger group instead.... For the 0.120" wall, I simply did both....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Trigger%20Group_zpslfjjiaef.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Trigger%20Group_zpslfjjiaef.jpg.html)
The radius on the top of the PRod trigger group is intended for a 7/8" tube OD.... When used on a 1.25" OD tube, the center of the arc doesn't touch, only the sides of the groove bear against the tube, and there is about a 1/32" gap in the middle because of the mismatch of the radii.... Using a 1-1/4" router bit (shown) I milled the groove out to a larger radius, removing metal from both sides of the top of the trigger group until the bit JUST touched the center of the hollow.... This eliminated the gap in the center of the groove when bolted to a 1.25" OD tube, and moves the trigger group up 1/32".... By using the tall sear, and machining the trigger, it works perfectly on a 0.120" (even a 0.130" wall tube)....
I'm getting closer to working on the hammers....
Bob
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I made my first hammer today.... I wanted to make these builds with a separate cocking handle, but I knew the hammer had to be longer than normal and was concerned that they would be too heavy.... I decided that the only way to find out was to make one and weigh it....
I started out with a 5/8" diameter steel core 2" long that was drilled in 1-1/4" deep with a 7/16" drill.... It had to clear the stop rod and allow for 1" of travel, which I hope to achieve.... I knurled the outside and took a piece of 1-1/8" diameter MDS from Rocker1 (thanks David) and drilled it out 5/8" and pressed it on so that there was a socket for the flange of the spring guide to fit into (it is less than 5/8" OD).... I turned the back end to length, leaving just over 1/8" of the MDS protruding past the steel.... The Delrin spring guide will push directly on the steel core, while the MDS outer will prevent the sear from popping up behind the hammer.... This is the rear view of the hammer....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Hammer%20Rear_zpsp3kq4ear.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Hammer%20Rear_zpsp3kq4ear.jpg.html)
The MDS was turned to 1.2" long from the back to the lower corner where the sear engages.... If that proves to be too long to cock, then I will either move the sear location on the hammer back, or machine a bit off the front of the SSG mount, there is a bit available there in front of the screw locations.... The front of the hammer is just the steel core, and the overall length is 1.70", which is about 1/2" longer than an MRod hammer.... This leaves enough material between the front of the hole and the front of the hammer for a cocking handle to be installed.... The handle was made from a piece of 7/32" drill rod that is 1.7" long.... Both ends are turned down to 3/16" for 0.40" length, and threaded 10-32, leaving a shoulder 0.40" from each end.... The hammer is drilled 1.50" from the back, through and tapped to 10-32, and counterbored 7/32" to a depth of 1/8" so that the shouldered rod bottoms below flush.... The knob on the handle was made from a piece of 1/2" OD black Delrin rod 1" long.... It was drilled 5/32" to 0.8" deep and counterbored 7/32" for a depth of 0.30".... and then the lower portion tapped 10-32.... This allows it to thread into the Delrin handle, which gets its strength from the steel rod, but keeps the weigh down.... I usually use a piece of aluminum for the knob, and 1/4" steel for the shaft, but wanted a lighter approach.... Here is the front view of the hammer and cocking handle....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Hammer%20Front_zps7fbtqj35.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Hammer%20Front_zps7fbtqj35.jpg.html)
The last step was to mill two 3/8" long slots in the sides of the MDS to allow the hammer to vent during firing, to make sure there is no pressure buildup on the front, or vacuum on the back.... The total weight of the hammer and cocking handle is only 58.7 grams, only about 10% heavier than the Steel and MDS hammer I use successfully on my BRods.... I have two other hammers for the BRods, an all steel at 104 grams, and an MDS with aluminum core at only 27 grams.... so I can go lighter or heavier should the need arise....
This hammer is made for the 6mm bottle gun, I need to make the other one smaller in diameter to fit the thicker wall tube.... After making this, I have one concern, and that is the slots milled in the sides allowing the hammer to cock sideways in the tube more easily, since the cocking force is on the right side, and aligned with the slots.... When I make the second hammer for the .257, which will be running higher pressure, I won't be quite as concerned about weight, so I plan two changes.... The MDS will be full length, with a notch milled in the bottom for the sear.... and it will have a single vent slot in the top only.... This will leave both sides circular, in case there is any tendency to cock sideways and bind when cocking with this hammer.... That way I can determine if there is any difference, and which is better....
Bob
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I made the second hammer today, for the .257, which has a slightly smaller tube ID.... The lengths are all the same as the hammer I made yesterday, and I have both in the photos for comparision.... Here is the top view....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Top_zpsxnhicdqt.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Top_zpsxnhicdqt.jpg.html)
Note that I moved only used one vent groove, on the top instead of the sides, so the hammer has more bearing area to resist any binding in the tube due to the side cocking handle.... In addition, I made the MDS full length instead of stopping it behind the cocking handle.... Here is the bottom view....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Bottom_zpsje7uvaxg.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Bottom_zpsje7uvaxg.jpg.html)
Instead of turning a 20 deg. bevel where the sear catches, I milled a flat to clear the sear and then milled the catch point on a 20 deg. angle to match the sear.... The new hammer is less than 2 grams heavier, and I like the appearance better, it looks like it should resist binding in the tube better than the first version with the shorter bearing length.... It's not worth changing the first one unless there is a problem, and having the two different versions will tell me if there is an issue with binding when cocking....
Bob
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Well today it finally starts to look a little bit like a gun.... and I got to find out that the hammer works as designed.... I measured two (dozen) times and then laid out and milled the cocking slot in the right side of the tube.... Here is what the long tube (intended for the tethered .257 cal) looks like now....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Long%20Tube%20with%20Hammer%20Slot_zps8lzf7fwt.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Long%20Tube%20with%20Hammer%20Slot_zps8lzf7fwt.jpg.html)
The hammer cocks and still has a bit of leeway for rearward movement before it hits the SSG mounting block that mounts the rear of the trigger.... When adjusted for 1.0" of hammer stroke, the front of the cocking handle rod is nearly 1/4" from the front of the slot when uncocked (as in the photo), so if I have the valve stem protruding 0.20" from the back of the valve (limiting the maximum lift to that, which is plenty).... and the stem touching the hammer when set for that 1" of stroke.... the hammer will hit the back of the valve body before the cocking handle hits the front of the slot.... which is what I wanted.... The hammer cocks smoothly and with relatively low effort with the 14 lb/in spring installed and about 5 lbs. of preload....
Now to lay out and machine the shorter tube for the regulated 6mm version to the same stage of completion....
Bob
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I got the trigger mounted on the short (regulated) tube, and milled the slots for the sear and cocking handle this afternoon.... This hammer works well also and I milled both the cocking slots 0.050" longer at the front.... With the handle at the front of the slot, you can see the back of the sear flush with the back of the hammer, so that is absolutely as far forward (maximum stoke) as I can go.... It is critical that the back of the hammer keeps the PRod sear pressed down, if it could pop up behind the hammer, the hammer would jam the valve open and dump the reservoir, and likely damage the hammer (or trigger) as well.... The length of the top face of the sear (about 1/8") is my safety margin....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Short%20Tube%20with%20Hammer%20Slot_zpsnwa0npva.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Short%20Tube%20with%20Hammer%20Slot_zpsnwa0npva.jpg.html)
This completes the stock, SSG and hammer assemblies on both guns.... Once I make a decision on the valves I will know where to mount them, and only after that can I proceed with the receivers.... Until I know where the valve exhaust port will be I can't make those.... The next steps will be making the front plug with fill fitting for the unregulated tube and the reversed tank block for the regulated one....
Bob
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Beautiful work so far Bob, as always!!
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I have often wondered about a long prod airtube to use for the AR style stock vs the adapters. Thinking out how to do all the adjustments was one of my concerns. Looks like you spent some considerable time thing about the solution. :)
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Well the 7/8" OD tube on a PRod is MUCH too small, and although the 1.25" OD of the MRod tube is large enough to machine down to 1.15" to fit inside an AR stock, if you did that the wall thickness on the tube would only be 0.045", which I think is marginal.... If you used steel for the tube, you might have enough strength not to kink if you fell on the gun, but with my tube being aluminum I thought it only a suitable solution for the long tube, which is 0.120" wall instead of 0.095".... That leaves me a 0.070" wall after machining....
I think part of the problem with fitting an AR stock to a PRod is that with the smaller tube ID (less than 3/4") and the short distance available for an insert to adapt that to an AR stock.... it makes the attachment a bit wobbly.... You could probably drill and tap the sides of the adapter and use a total of 4 screws to eliminate that issue.... Alternately, as you say, you could have a custom longer tube made, and then sleeve it up to 1.15" OD using aluminum or even plastic so that the weight wouldn't increase too much.... Then you still have to deal with the adjustment and preventing rotation, but the solution I used would work for that....
Bob
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Yep, I have a number of the adapters and they all seem to loosen over time. You can't make a permanent fix without addressing the adjustment issue. Was thinking a larger tube over the prod but never took those thoughts any further. ;)
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The stocks wobble around over the buffer tube, so there is always slack there anyways.... part of having an adjustable stock....
Bob
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The stocks wobble around over the buffer tube, so there is always slack there anyways.... part of having an adjustable stock....
I have used a plastic shim between buffer tube and stock to help with that wobble. On the Prod, with the added adapter length, the "collapsible" aspect is severely limited, so locking it down doesn't cause me issues.
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I made the front plug and fill fitting for the long tube today....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Fill%20Fitting_zps9r1dulnx.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Fill%20Fitting_zps9r1dulnx.jpg.html)
It is a piece of 1" diameter 2024-T3 that is 1.4" long.... It is drilled through 1/8" for an air passage, and then drilled and tapped for four 10-32 x 1/4" long SHCSs with the head in shear to take the loads.... There is a single O-ring groove for a #117 O-ring.... The front is drilled and tapped 1/8"-27 NPT for a male Foster, and the back is drilled out a short distance to 5/8" just to gain back part of the volume lost to the plug.... I drilled the four 5/16" retaining holes in the tube at a 45 deg. angle to the vertical, so that the front plug can be removed without removing the barrel....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Reservoir%20End_zpsysjwtdvm.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Reservoir%20End_zpsysjwtdvm.jpg.html)
I'm quite pleased with this, the next job is to ponder how to make the reversed tank block for the short tube to hold my 500 cc Carbon Fibre bottle under the tube....
Bob
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Today I tackled the job I hate the most, but possibly the most satisfying if it turns out well.... I turned the stub and rear face of the tank block.... The piece I started with was a 1-1/4 x 3-1/2" piece of 6061-T6 rectangular bar stock.... I roughed out the stub material with my power hacksaw (finished with a hand saw) and then cut a piece 2-3/4" long, ending up with an "L" shaped piece of aluminum.... The small part of the "L" is for the round stub that inserts into the front of the tube, so I had to mount it in the lathe to make that round and the correct diameter, and cut the O-ring groove.... In the same operation, you face the rear surface of the block flat square to the stub.... The trick was mounting it in my lathe....
I have a 4-jaw chuck, with reversible jaws, but with them in the normal orientation one jaw was right out past the chuck face, because the block has to be offset so that the round stub is at one end.... I reversed that jaw, which solved that problem, but then the block has to sit on top of the first ledge on the jaw, and I didn't like the idea of trying to shim the block at the other end, there is incredible load when turning this piece, and it must be very rigidly mounted.... or it could jar loose and come flying out of the lathe, or break something (and maybe me).... I came up with the idea of reversing the opposite jaw as well, so that the block would sit on both of them, but NOT reverse the side jaws, so that they had more clamping area.... it worked perfectly, as you can see below.... Top and bottom jaws reversed, side jaws "normal"....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Turning%20the%20Tank%20Block_zpsex2kaxmr.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Turning%20the%20Tank%20Block_zpsex2kaxmr.jpg.html)
Before putting the block in the chuck, I laid out and drilled a center hole for the stub, using a 60* center drill.... The by using a 60* center in the tail stock, pressing the block against the two reversed chuck jaws, it was pretty simple to get it centered.... I have never turned such a large, offset block before, and the impact with the tool bit is considerable if you take too big a bite.... so I used the slowest feed rate (0.004") and could only remove 0.005" per pass off the flat surface beside the stub.... I had left the material 1/10" oversize, so that took 20 passes at over 3 min. each.... well over an hour just to machine that flat surface.... Then I had to turn the 1-1/4" square stub that was sticking out to a 1.05" circular one, drill the center air passage (1/8") and cut the O-ring groove.... Between the setup and machining, it took all afternoon, and some of the evening.... I must be the world's ~ s l o w e s t ~ machinist.... ::)
It was pretty nerve-wracking, so I will have a good sleep and tackle the rest of the block tomorrow....
Bob
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Nice setup Bob, if there is a will there is a way! :D
Marko
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I think I cringed for over an hour straight, every time that piece of aluminum came around and smacked the tool bit.... and I was only running at 166 RPM....
Bob
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Ever considered buying a mill with rotary indexing table?
Marko
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Boring head is useful in these situations and it is easier to set up than rotary table.
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Too much money for my very limited retirement income, guys.... I don't even have a Mill, just the milling attachment for my lathe you can see in the background of that photo....
Bob
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I finished the tank block today.... My 300 bar, 500cc Carbon Fibre tank clears the main tube by just over 1/16" when installed.... Here is the side view, showing the regulator installed....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Tank%20Block%20Side_zpsemhjmm6q.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Tank%20Block%20Side_zpsemhjmm6q.jpg.html)
The notch on the top front is for a barrel band, there are two 6-32 holes drilled and tapped on the front face to attach it.... As you can see, there is a Picatinny rail on the bottom.... The hole there is for the plug for the vertical air passage.... The plug is a low-profile 10-32 SHCS with a # 008 O-ring under the head in the milled 5/16" recess.... There are four 10-32 screws to retain the stub of the tank block in the tube, again drilled at a 45 deg. angle so that the tank block can be removed without removing the barrel.... The stub seals into the tube with a single # 118 O-ring.... The 1/8"-27 NPT tapped hole in the side is for a gauge for the pressure downstream of the regulator.... Below is the rear view....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Tank%20Block%20Rear_zpscwzynwit.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Tank%20Block%20Rear_zpscwzynwit.jpg.html)
The method of mounting the regulator is different from common practice.... Instead of using the two (red) O-rings inboard of the threads in a bored hole, the hole in the block is simply drilled deep enough to clear the length of the regulator and tapped 1/2"-14 NPS.... At the top of the hole is a recess milled with a 7/8" end mill to a depth of 0.085" to accept a # 115 O-ring.... This is a snug fit over the regulator, in the groove between the threads and the shoulder on the bonnet, which is 0.900" OD.... When the regulator is tightened into place, that O-ring fits into the groove in the tank block, and seals the regulator outboard of the threads.... This trick, pioneered by Travis, is much easier to machine, and is used on the Flex and Cobra.... Qudos to him and Jim Gaska for coming up with the idea.... The three 5/8" wide grooves milled around the middle of the tank block and the back and sides are only to remove a bit of weight, and pretty it up a bit.... Even so, the block weighs a hefty 8 ozs.... ::)
Bob
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I have no Idea how you pulled that off with just a lathe but Im giving you a standing ovation!!! Bravo. That must of had a pucker factor of 10 at least.....
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Boring head is useful in these situations and it is easier to set up than rotary table.
Well I dont see anything difficult setting up my rotaries, horizontal or vertical.
Boring head would work also.
Marko
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I have no Idea how you pulled that off with just a lathe but Im giving you a standing ovation!!! Bravo. That must of had a pucker factor of 10 at least.....
You are right Travis, imagine what Bob would build if he had a proper mill.
Marko
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Travis, setup takes longer than machining on a job like this.... Thanks for the praise, buddy.... Hope your back surgery goes well....
PS, I'm just about ready for the regulator and valve.... ;) :P
Bob
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I have no Idea how you pulled that off with just a lathe but Im giving you a standing ovation!!! Bravo. That must of had a pucker factor of 10 at least.....
LMBO., until I did the reading , I thought bob simply permanently attached a cylinder to the block , and had to go back to turn the cylinder. The fact its all one piece is BONKERS, and the interrupted cut time must have been hours !
Bob, I just read that you sawed off some material beforehand, that's good to hear.
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Well I may be SLOW, but I'm not stupid.... *LOL*....
Bob
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A couple of days ago I got a start on one of the valves.... got it roughed out, made some parts for the inside, and then spent a day finishing off the design.... Today I finished the first valve.... Here is the inside roughed out.... The valve is 5/8" ID with a 5/16" throat and a 1/8" stem....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Valve%20Inside_zpsjwxaybsx.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Valve%20Inside_zpsjwxaybsx.jpg.html)
The spring retainer end cap is a vented wheel that fits into a recess in the front of the valve and is retained by an circlip.... The area for the wheel is 3/4" ID.... I made the 3/8" thick and machined out the inside, leaving a 1/8" vented web.... That was my solution to the difficulty of holding a 1/8" thick part for machining....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Valve%20Recess_zpses2sejxn.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Valve%20Recess_zpses2sejxn.jpg.html)
Here is a front view of the completed valve.... The two long 6-32 screws are the front mounting bolts for the receiver.... They penetrate the valve BEHIND the valve seat, straddling the throat, which allows me to use larger screws than an MRod valve and yet have a larger ID....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Valve%20Front_zpstx1ikiwq.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Valve%20Front_zpstx1ikiwq.jpg.html)
The O-ring is located behind the recess for the wheel, where the valve wall is full thickness.... The gauge is tapped directly into the left side of the valve, behind the O-ring, so no need to drag it across a large hole in the tube.... Here is the back view, showing the huge 0.257" port, which is on a 30 deg. angle towards the 5/16" throat for improved flow....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Valve%20Back_zps0vagpjcu.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Valve%20Back_zps0vagpjcu.jpg.html)
The four valve mounting bolts are 10-32 x 1/4" SHCSs set down with the heads in shear.... They are in staggered pairs, the top and bottom pair in a similar location to an MRod valve, but the ones on the sides are 1/4" further forward.... I had to do that to make sure there was enough tube material for proper strength on the RH screw, which sits ahead of the cocking slot for the hammer.... The slot ends exactly at the back edge of the valve body....
The reason for no photos of the inside is that this valve is my own home-made version of the ART/SS valve.... Since I was privy to the development of it, I was able to design and make my own version.... but out of respect for Travis, I am not divulging the details until he gets his patent in place.... My sincere thanks to Lloyd and Travis for their help while I was making the very intricate guts for these valves.... I made several versions before I managed to get any parts that were even usable, they are, to say the least, challenging.... and well worth their price, IMO....
Bob
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Wow that is some mad skills and well thought out to boot. This will be fun to watch. Following
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Nice work Bob, I was looking at the pictures first and was thinking that looks like ART valve right there.
Then I read the text and was ok it is bob art valve. ;)
Will be interesting to see the strings and groups on this one for sure.
Bob do you thread the bolts around transfer port to the tube also or just to the valve body?
On smaller bore the end of the valve is not so critical but when making a bigger bore they see pretty substantial force from the valve and I would use threads instead of the c clip.
Don't ask me how I know. ;D
Marko
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The two 6mm vertical screws are threaded into the valve body only, like an MRod.... They hold the receiver against the tube, which has through holes, pinching it against the valve....
I can't imagine that the front end of the valve in an ART/SS design is subject to much end force, and both Lloyd and Travis use a circlip.... but if I have a problem then I can't say I wasn't warned.... Thanks for the heads-up....
Bob
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Well not on small calibers, it won't be a problem but something past 500-600fpe and big valve you start seeing some stress on those parts.
Thanks for the answer on the bolts, I usually thread them together tube and valve.
Was just curious that's all.
Marko
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Well not on small calibers, it won't be a problem but something past 500-600fpe and big valve you start seeing some stress on those parts.
Thanks for the answer on the bolts, I usually thread them together tube and valve.
Was just curious that's all.
Marko
Were all a long way off from your kind of power Marko so its not and issue for us. Someday Ill step it up and take a wack at a BIG BORE!!
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That will be an interesting build to follow Travis. :D
Marko
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That will be an interesting build to follow Travis. :D
Marko
You better hope I dont because I would be PMing you 10 times a day asking How you did this or that LOL.
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Naah, I think you'll figure it out just fine, the art valve tells me that much. :D
But yeah, asking the right questions is not forbidden. ;)
Marko
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Today I drilled all the holes for the valve in the long (unregulated) tube.... Here is the right side....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Right%20Side_zpskqpudz7a.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Right%20Side_zpskqpudz7a.jpg.html)
You can see the cocking slot for the hammer, and now you can see why I moved the side valve mounting holes forward, to give lots of material between it and the front of the slot.... here is the left side....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Left%20Side_zps0reyye4s.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Left%20Side_zps0reyye4s.jpg.html)
You can see the large hole for the gauge on the side.... I installed the valve, hammer, SSG assembly and trigger group today and tested everything.... With the hammer set for 1" of travel I still have 0.22" between the front of the hammer and the back of the valve, and about 1/16" between the cocking handle and the front of the slot.... This allows for 0.20" of maximum lift and still have a 0.020" gap for the SSG.... The valves have an internal travel of about 0.24", so with the stem protruding 0.20" the hammer will hit the back of the valve before anything else hits and gets damaged.... I also made the second valve body today....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Two%20Valves_zpsiuyalz6k.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Two%20Valves_zpsiuyalz6k.jpg.html)
The one in the foreground is for the shorter regulated tube.... Since there is a gauge downstream of the regulator in the tank block, there is no hole in the side of the valve for a gauge like there is in the valve for the unregulated tube in the back.... The valve in the front is also larger in diameter because the regulated tube is 0.095" wall instead of 0.120" wall....
Bob
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Last day in the shop before Christmas.... I tidied up all the loose ends.... no photos because there was nothing new, just a second batch of what I have already made.... I built all the internals for my second ART/SS valve (my version), and drilled the holes in the short (regulated) tube to mount the valve.... Other than cut that tube to length (after I get the regulator for my 500 cc CF tank) and drill the 4 holes to retain the tank block, both "lowers" are now pretty much finished.... I am waiting for some 70D O-rings, once they arrive I will be able to assemble and pressure test them.... Oh, I forgot I still have to lap the valve seats and make sure the poppet face is square....
I finalized the design for the receivers today.... The material I bought wasn't tall enough to allow for slope in the scope dovetail, but fortunately I have enough 1 x 1.5" aluminum bar stock for the two receivers.... The scope rail will be angled 20 MOA to put the scope pretty much on optical center with a POA of 100 yards.... These are both single-shot guns, and I wanted to make both receivers identical and yet set one up for 6mm and the other for .257.... I plan to use an "L" shaped insert in the loading area, sized for each caliber, that will bolt into place.... The left hand wall of the receiver will be full height to increase rigidity, the bullet will load from the right, like on my Monocoque.... at least that's the plan at the moment....
I want to wish all my friends here on the Forums all the best for a Merry Christmas and a Happy New Year.... 8)
Bob
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.. The scope rail will be angled 20 MOA to put the scope pretty much on optical center with a POA of 100 yards....
I want to wish all my friends here on the Forums all the best for a Merry Christmas and a Happy New Year....
Bob
Bob,I agree with you absolutely and in the new year I will be really happy to see your 100 yd targets from this future gun. Wow.
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hey bob , happy holidays .. quick question since I cannot find the answer, what barrel will this be ??
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Barrels are detailed in Reply #83 on page 5.... TJ's 6 mm & .257, both in 10" twist, with a 14 mm OD and a 20mm OD CF sleeve over them....
Bob
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thanks Bob !!
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When do you expect to see the orings for the valve Bob? Eagerly awaiting this build.
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I have been cleaning up some leftover projects for the last month while I have been waiting for some 1.2 mm CS O-rings to arrive for the poppet in my version of the ART/SS valve.... They finally got here and I made a new poppet which worked out great.... The smaller O-rings allowed a shallower groove, which I moved further down the poppet towards the seat and now it seals great and seems to function fine, even at 4200 psi.... It is holding air pretty well, losing less than 100 psi per day, which is good enough for now, and often slow leaks like this improve with time, as they are often the poppet on the seat.... Anyways, assuming it is good enough for now, the next order of business is to make the uppers, and then ream the chambers and mount the barrels.... After that I can shoot these guns for the first time, as I cast some bullets last week as well....
I started on the receivers yesterday, cut them to length (actually 1" over) and machined the concave bottom to fit against the tube on both receivers, which will be interchangeable on the lowers.... Today I laid out and center-drilled both ends of the bore for the barrel and bolt, high enough above the top of the tube to allow for the 20 mm OD barrel sleeve, plus 0.20" to allow for the thickness of a piece of 1-1/4" ABS pipe which I will be using for the foregrip on the unregulated .257 cal.... That plastic pipe is 0.150" wall, so it will just nicely clear the Carbon Fibre barrel sleeve.... It will be captured between a recess on the bottom of the receiver and the tube, like I did with the foregrip on the Monocoque.... Anyways, the C/L of the bore is 0.60" above the top of the main tube.... Once the locations were center-drilled, I mounted the receiver between centers on my lathe, and then held the back in my 4-jaw chuck.... Having it sit on a 60 deg. center inside the spindle bore allows easy centering of the jaws, you just tighten them progressively on the four side of the receiver until it is secure.... Using a live center (ie one that spins on a bearing) in the tailstock, I machined a 1" long collar on the front of the receivers (which is why I left them 1" too long).... The collars will ride in my steady-rest to support the receivers on center while I drill them full length....
I first drilled a 1/4" pilot hole from front to back, using a foot long 1/4" drill bit, stopping just before I hit the 60 deg. center in the headstock.... I then used a long 1/2" drill to increase the diameter to the finished size, removed the receiver from the lathe (so the 60 deg. center wasn't in the way, and drilled through the last 1/2" at the back.... The hole was straight and true, and parallel to the top of the tube in both planes, which is what I wanted.... A piece of 1/2" CRS slides perfectly through the receiver, full length, so I know that the bolt and the barrel will be aligned and parallel.... I them mounted the receiver back in the lathe between centers, re-checked the steady-rest position, and then drilled the front of the receiver out to 25/32" to accept the 20 mm CF barrel sleeve.... The sleeve is about 0.004" larger than the drill size, but it just starts into the hole, so all it will need is a bit of sanding to be a perfect slide fit.... Here is what it looks like at the moment.... I only have one drilled at the present time, the other one will be done tomorrow, all going well....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/6mm%20257%20Receiver_zpslrskmram.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/6mm%20257%20Receiver_zpslrskmram.jpg.html)
The plan is to cut off the collar, it was only there to allow me to support the front of the receiver in my steady-rest.... I don't need it for support, as the barrel sleeve goes 2.5" into the receiver, which is over 3 diameters.... It will be located by two sets of 3 setscrews at 120 deg. so the assembly should be 100% rigid when complete....
Bob
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The plan is to cut off the collar, it was only there to allow me to support the front of the receiver in my steady-rest.... I don't need it for support, as the barrel sleeve goes 2.5" into the receiver, which is over 3 diameters.... It will be located by two sets of 3 setscrews at 120 deg. so the assembly should be 100% rigid when complete....
Bob
Nice work, Personaly I will let the collar.
I really want to sea haw CF sleeve barrel will work.
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The only significant problem with the collar is that I have to machine most of it away at the bottom where the plastic pipe will be for the forestock.... That would only leave about a 1 mm wall thickness in the center at the bottom.... Since the CF sleeve is inside the receiver by over 3 diameters without the collar I don't think it really has any benefit.... I haven't decided yet, one way or the other....
Bob
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I drilled the other receiver today, and then drilled and countersunk all the mounting holes and drilled through for the transfer port....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Two%20Receivers_zpsqhr7ndbr.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Two%20Receivers_zpsqhr7ndbr.jpg.html)
The small recess on the bottom just behind the transfer port is to clear the upper valve mounting screw, which is just proud of the tube.... The receivers, like the tubes, are drilled on the same pattern, so the uppers will be interchangeable on the lowers.... Although I intend to build the .257 on the long, unregulated tube with the thick wall (4200 psi MSWP) and the 6 mm on the regulated bottle version with the short tube (thinner wall with 3200 psi MSWP).... the interchangeability will allow me to test the other way around, and change my mind should I decide to....
Bob
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The countdown has begun 4,,,,,3,,,,,,2,,,,,,1,,,,,,,Launch!!! This is getting good now. What do you think 1 week or so to launch?
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More than that I think.... I still have to chamber, port, crown and sleeve the barrels (still have a 6 mm reamer to make) and install them in the receivers.... Plus there is a lot of machining left on the receivers.... bolt "J" slots, port adjuster, loading area, barrel retention.... and make the bolts, handles and loading platform inserts.... The receivers will be the same, but there will be different loading platform inserts for the 6 mm and .257 cal.... In addition, after the first test I will have to make the second set of guts for the other valve.... and hopefully not have to redesign it....
Plus I'm waiting for a regulator.... *poke*....
Bob
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Today I milled out the loading port area in the two receivers.... Instead of milling it straight across, I left the left-hand side of the receiver intact from the boreline over, so that I don't lose so much rigidity.... These guns are single-shot, so no need to cut it away more than that.... I did this on my Monocoque and it works well, but of course you must load the bullet from the right side.... Drilling a 1/2" hole straight through the receiver to assure the alignment of the bolt and barrel means that when you machine the loading port you don't have a tray to guide the bullet into the bore.... so that is made from a separate piece of 1/2" diameter steel.... I drilled one for 6 mm and the other for .257 before milling them to shape.... You can see one of the inserts sitting on top of the receiver in the foreground.... along with a flat-head 4-40 screw which holds it in place.... The back receiver already has one installed....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Loading%20Ports_zps7qy8s6pr.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Loading%20Ports_zps7qy8s6pr.jpg.html)
With the loading tray in place, the right side is level with the centerline of the bore.... and the left side is vertical, tangent to the left side of the bore.... You don't need to look at what you are doing to load, just place the bullet on the right hand lip of the tray, and roll it to the left and close the bolt....
Bob
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I got lots more done on the receivers today.... This reduced the weight of them quite a bit.... and vastly improves the appearance....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Receivers%20Shaped_zpsqckw5end.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Receivers%20Shaped_zpsqckw5end.jpg.html)
The top and upper edges are now milled down, leaving raised areas where the dovetails for the scope mounts will be.... I also bevelled the top corners as well.... When I machine the dovetails I will be angling them down 20-25 MOA at the front to put the barrel on POA at 100 yards with the scope still optically centered....
Bob
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Excellent Bob! As always!
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Coming along nicely, looking forward to more!
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Looks good Bob, nice to make parts in series.
Marko
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I worked on the receivers more today.... I drilled and tapped the six holes for the set-screws that will secure the barrel.... The original plan was for 10-32 screws at 120 deg. to each other.... but I was unable to get them of the proper length here in town, but I was able to get 5 mm x 0.8 mm Metric setscrews that are 10 mm long.... You can enlarge 10-32 threads to M5 by simply running the tap through them, as they are the same pitch (within less than 1%) and the Metric screws are 0.008" larger than the 10-32s.... I dislike mixing SAE and Metric fasteners on a project, but the alternative would have been to wait weeks to get the 10-32s.... I justified it by the fact that the barrels are 14 mm and the CF sleeve is 20 mm OD.... so at least everything to do with the barrels is Metric.... ::)
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/J%20Slots_zpsfqmsiviy.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/J%20Slots_zpsfqmsiviy.jpg.html)
I had one other little glitch when setting up to drill the lower holes for the setscrews.... In order for the receiver to clear the carriage on my lathe (I was using my milling attachment to drill and tap the holes accurately) I could not drill them 30 deg. below the horizontal, I had to use 35 deg.... This is of no practical importance, but means that the angle from the top to each side screw is 125 deg. and the angle between the bottom screws is 110 deg.... instead of them all being 120 deg....
I also set up and milled the slots for the bolt handle today.... The front receiver is finished, but dinner hit the table before I got the vertical part of the rear slot done.... I'll do that tomorrow before I set up to fly-cut the recess in the front bottom of the receivers to locate the plastic pipe of the forestock....
Bob
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Every build has a glitch, it's nothing new. I too hate mixing metric and sae fastners, thats why I dont use sae. :P
Marko
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"Officially" Canada is on the Metric system.... but if you go into any Industrial Supply, you will find 90% SAE fasteners, and VERY few Metric.... That is why I always work in SAE, plus in the USA (where I also buy fasteners) Metric is even more rare.... I got caught out this time, went in to get the 10-32 setscrews and all they had was 10-24 (and I had already started tapping the holes 10-32).... I just got lucky that they had the M5 setscrews in the length I needed and I had the tap to convert them....
Bob
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Here are the receivers with everything now done except to machine the 20-25 MOA slope in the scope mounts and cut the dovetails in them....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Recess%20and%20Velocity%20Adjuster_zpss1zcdvxd.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Recess%20and%20Velocity%20Adjuster_zpss1zcdvxd.jpg.html)
On the lower front corner you can see the semi-circular recess milled to act as a clamp for the plastic pipe forestock.... It pinches the pipe between the bottom of the receiver and the main air tube, mounting it solidly at the back in the lowest possible position so that it doesn't rattle around, and clears the barrel.... The velocity adjusting screws are installed in the back, in line with the lower bolt slot.... The 8-32 SHCS pushes on a 1.5" long steel pin that can prevent the bolt handle from retracting fully in the slot.... I have about 10 turns of adjustment, the back receiver has the adjuster fully retracted (maximum velocity) and the one in front has the adjuster set to minimum velocity.... I labelled the steel pin which is sticking out into the lower bolt slot, which holds the bolt forward so that the nose obstructs the barrel port, reducing airflow (to almost zero when fully closed as shown).... You can't see it in these photos, but there is a vertical hole coming up from the bottom, in line with the bottom of the adjusting screw.... It is tapped for a 6-32 setscrew which presses on a 1/4" long piece of thin Teflon rod which acts as a brake to prevent the velocity adjusting screw from moving by itself....
Bob
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I got to work on the barrels today.... The first order of business was to machine the breech end to 1/2" OD for 1" of length so that it will fit into the receiver.... In addition, I had to machine down the OD of the carbon fibre tube slightly to fit inside the 25/32" forward section which is drilled to a depth of 2.5".... I did that with the end of the tube running on a live center in the tailstock of the lathe to insure concentricity between the ID and OD, and it worked out great.... Both the CF sleeve and the barrel slide perfectly into the receiver and can be rotated individually, showing they are concentric with each other and the holes in the receiver are as well.... This was a bit of a nervous time, as any inaccuracy there would have been hard to correct.... At the muzzle end I turned the barrel down to 1/2" as well and threaded it 1/2"-20 NF so that it can accept either a Hatsan Air Stripper (as a backup) or my intended Harmonic Tuner, which I have yet to make.... Here is a photo of the barrel ends, breech on top, muzzle below....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Barrel%20Ends_zpsdvgtnbvh.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Barrel%20Ends_zpsdvgtnbvh.jpg.html)
and here is a photo of them with the CF sleeve in place (but not bonded yet)....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Sleeve%20Ends_zpsajbx6rsa.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Sleeve%20Ends_zpsajbx6rsa.jpg.html)
You can see where I had to skin down the outside of the CF tube to fit the 25/32" hole in the receiver, just a few thou was all that was required.... The next job will be to cut the chambers in the barrels before bonding on the CF sleeves.... I think the reamer I made for my .257 Monocoque will work, but I will have to make a new chamber reamer for the 6 mm.... I received some samples from Nick at Nielsen Specialty Ammo in the mail today (perfect timing, thanks Nick), as I would like to make sure the chamber in the .257 will accept as many different bullets as possible.... Here is a photo of the selection of .257 bullets I now have to try....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/257%20Bullets_zpsr8irkv1r.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/257%20Bullets_zpsr8irkv1r.jpg.html)
Left to Right they are.... My 98 gr. BBT HP, the 91 gr. Noble from Nick and his 85 gr. rebated boattail HP, an 88 gr. RCBS 82301, an 82 gr. NOE 260-80 FN, and a 73 gr. Lyman 257420.... I can also cast HP versions of the 82301 and 257420, so I will have lots of bullets to choose from.... I don't expect the 98 gr. BBT (or the FN version of it) to work in the 10" twist of the TJs barrel I have.... so if the chamber has to be too short to fit all the other bullets for it to chamber, so be it.... but just looking at the position of the ogives in the above photo, I think I can cut a chamber that will work with all of them.... If anything, the bullet with the Ogive starting the furthest forward is Nick's swaged HPBT.... Here are the 6mm Bullets.... the TJs barrel I have is also 10" twist....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/6mm%20Bullets_zpsovyvnprm.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/6mm%20Bullets_zpsovyvnprm.jpg.html)
Left to Right they are.... 58 gr. Bowman HP from Arsenal, 59 gr. NOE 245-64 HP and 69 gr. NOE 245-74 HP.... I can also cast FN versions of all three bullets.... The weights of the FN versions are 61 gr., 63 gr. and 73 gr. respectively.... The 63 gr. NOE is a shortened, FB version of the 73 gr. beside it, with the GC shank removed.... I also have a mould for a 65 gr. shortened version of the NOE 260-80, done the same way, but that will be too light for the power of this .257 cal (I hope)....
Bob
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I worked on making the Harmonic Tuners today.... I got two of the brass weights made, and one of the mounts that screws onto the muzzle.... Here is what it looks like when assembled....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Harmonic%20Tuner_zpsejrausfr.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Harmonic%20Tuner_zpsejrausfr.jpg.html)
The threads are 15/16"-28.... I like 28 TPI for this job because 10 deg. of rotation is 0.001" of movement (1 "hour" on a clock face is 0.003", 1 turn is 0.036").... The brass weight is made from a piece of 1.5" bar stock 1" long, the setscrew presses on a short piece of Teflon rod which acts as a brake to prevent the weight from moving by itself.... The mount is made from a piece of 1" CRS.... There is a small collar of that diameter at the front, with a 3/16" hole drilled though it to allow it to be tightened onto the muzzle with a short piece of 3/16" bar stock.... The remainder is threaded, the 2" of threads giving over 1" of adjustment for the weight.... The center portion is threaded inside 1/2"-20 NF to thread onto the barrel, and the back is counterbored 0.80" ID for 1" of length to fit over the CF sleeve.... The front is drilled out 3/4" ID, it only projects 1/2" past the muzzle to allow the HPA from the shot to escape quickly without affecting the bullet.... and it also serves to protect the crown which is a simple 90 deg. angle....
The mount weighs a couple of ounces, and the movable brass weight weighs just over 5 oz. at the present time, although I may put chamfers on the corners for appearance after initial testing.... I'm really looking forward to trying this system, I know it is tremendously successful in rimfire benchrest, where it can drastically affect the group size....
Bob
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Here are the completed harmonic barrel tuners.... The muzzle of the barrel is about 3/8" inside the front of the mount, about where the outside threads start....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Harmonic%20Tuners%20With%20Scale_zpsenzsxvtc.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Harmonic%20Tuners%20With%20Scale_zpsenzsxvtc.jpg.html)
The scale is like a clock face, with the quarters having longer index marks.... with 12 o'clock being where the setscrew is.... Each mark equals 0.003" of movement on the tuning weight.... By starting with the weight against the shoulder at the front, you can record the position using "hours" for the turns and "minutes" for the index marks, so 9-1/3 turns I would record as 9:20.... and 15-3/4 turns as 15:45 etc.etc.... I'm really pleased with the way they turned out....
Bob
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This is awesome Bob! Posting to keep updated on your progress
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I am in awe on this project...
and want to thank you for your support of the community and taking the time and effort to expand the knowledge base of the HPA/PCP community.
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Still dreaming about finding a 26" Remmy 722 1:12 .244 barrel.. ;)
I think it would work well up to about 70g...
of course I keep watching.. ;D
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I cut the chamber in the .257 barrel today, using the reamer I made for my Monocoque....
(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/257%20Monocoque%20Chamber%20Reamer_zpsj1ordmct.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/257%20Monocoque%20Chamber%20Reamer_zpsj1ordmct.jpg.html)
Here are all the bullets that will fit.... They were all chambered to a depth of 0.60" from the end of the barrel, which will put the base just ahead of the front of the barrel port.... All bullets were sized to 0.257" before testing how they chambered.... When the chamber is too short, you sure know it, as you have to push hard enough to mark up the base, and it's pretty obvious when you get the length right....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/257%20Bullets_zpshef0w8ul.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/257%20Bullets_zpshef0w8ul.jpg.html)
I enhanced the contrast as much as possible so that you can see the rifling marks, but they are still hard to see on all except the longest two BBTs (112 gr. FN and 98 gr. HP), where they are clear on the back of the head.... The shortest bullet is the Lyman 257420 73 gr. and it barely touches the leade.... If you push it in by hand, you can only feel resistance for about the last 1/16", and basically cannot see any marks, even with a loupe, unless you push it in another 1/16", where you feel significant resistance.... I don't expect the two longest bullets to work in the 10" twist in this barrel.... but since I can chamber them I will be able to test that and prove or disprove the validity of the Kolbe Twist Calculator numbers for them.... Many of my BBTs seem to be stable in a slower twist than it gives, so there is a chance that the 98 gr. HP may work.... providing I have enough power to push it....
The other four bullets all slid in between 0.50-0.54" and then took a bit of a push (not much, mind you) to seat them to 0.60".... If you look carefully you can see shallow marks from the tapered leade, which they are sitting firmly against when chambered.... Those 4 bullets, from L to R, are the 91 gr. Noble, the 85 gr. NSA BTHP, the 88 gr. RCBS 82301, and the 82 gr. NOE 260-80 FN.... If I find one particular bullet shoots the best and want to play with different seating depths, I can do that by changing the length of the bolt nose....
Next step is to make the bolt, cut the O-ring groove and polish the chamber behind the barrel port.... then cut the CF sleeve to final length and glue it on.... and then machine the barrel port.... I was very pleased with the way the 3-flute reamer worked, so I am going to copy that design when I make the one for the 6mm barrel.... just smaller diameters for the pilot and chamber of course....
Bob
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Odd numbered reamers usually work well, odder the better. I once made a 5 flute reamer and by accident got the flutes unevenly divided, so that the width of tooth wasn't even close to same but it worked so much better than the correctly made one that I ended up using that. Btw what do you use for chamber polishing and what level of accuracy and surface finish ("RA"/μm) is achieved?
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Awesome work Bob. I'm just in awe of you work and attention to detail.
Peter
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I made the 6mm reamer this afternoon.... still not hardened and tempered but it turned out dimensionally accurate....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/6mm%20Reamer_zpsrojpc1lb.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/6mm%20Reamer_zpsrojpc1lb.jpg.html)
It is made from O1 Drill Rod.... The next step is to heat it to cherry red and quench it in oil to harden it.... Then I will polish it, hone the cutting edge again, and then temper it in the oven.... tomorrow's jobs....
Albert, I couldn't tell you what the finish on the chamber is.... Yes, I understand that unevenly space flutes actually work better than symmetrical ones.... but I just mill the flutes in mine in 5C collet in a hex block, skipping every other flat.... I plunge the end mill 5% of the caliber below the centerline to create the relief angle.... That creates a very fine cut, so cutting the chamber is slow.... I run the lathe at 28 RPM and continually pull the reamer to clean it of the dust sized metal particles the reamer creates....
Bob
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Here is what the finished reamer looks like....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Tempered%20Reamer_zps2bub7oat.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Tempered%20Reamer_zps2bub7oat.jpg.html)
It was hardened, polished, and them tempered for 30 min. at 465*F, raising the temperature to 480*F for the last 5 minutes because it was a little too pale a straw colour.... The result is a nice brown, the way I like my reamers....
Bob
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Nice, Bob! An that would make it about Rc 60?
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No idea....
Bob
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No idea....
Close: http://www.buffaloprecision.com/data_sheets/DSO1TSbpp.pdf (http://www.buffaloprecision.com/data_sheets/DSO1TSbpp.pdf)
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Just found that, because you made me curious.... Here is their tempering chart for O1 tool steel, which is what I used....
(http://i378.photobucket.com/albums/oo221/rsterne/Parts%20for%20Sale/O1%20Tempering_zpsmnozmm8i.jpg) (http://s378.photobucket.com/user/rsterne/media/Parts%20for%20Sale/O1%20Tempering_zpsmnozmm8i.jpg.html)
So, yep, about RC 60 would seem correct.... not that I have any real idea if that is the best for the job or not.... *LOL*....
Bob
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It's always a nervous time when you first use a new chamber reamer.... They seem to get smaller through the polishing, hardening and repolishing, and I'l always wondering if it will cut the chamber to the right diameter.... When I set up to cut the chamber in my 6mm barrel today and starting advancing the reamer, it went so easy I thought "carp, it's too small".... I cut the leade into the barrel about 1/4", and then pulled it out.... To my surprise, and delight, I found that it cut better than any reamer I had ever made before, and the little channel between the flutes that I had filled with oil had a nice pile of shavings sitting in it....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/6mm%20Reamer%20Cutting%20Well_zpsfy9jj49s.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/6mm%20Reamer%20Cutting%20Well_zpsfy9jj49s.jpg.html)
Usually you can "feel" quite a bit of resistance on the handwheel on the tailstock as you feed the reamer in, the barrel gets warm, and the shavings are not much more than dust size.... Not so with this reamer, the shavings were like little needles, about 1/16" long and 0.005" in diameter or so.... I could actually feel the "bump-bump-bump" as each flute hit the rifling lands and slowly carved them away.... I don't know why this one is so much better.... but I hope they all come out like this from now on.... It may be that I honed it just right.... I know I will try the same honing technique on another reamer the next time, to see if that was the difference.... I sure hope so, this one cut a beautiful chamber in short order.... Here are the three 6mm bullets I used to set the length....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/6mm%20Chambered%20Bullets_zpsxkbhzazg.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/6mm%20Chambered%20Bullets_zpsxkbhzazg.jpg.html)
Left to Right are the 63 gr. NOE 245-64 FN.... the 61 gr. Bowman by Arsenal.... and the 73 gr. NOE 245-74 FN.... The 63 gr. is a shortened version of the 73 gr., with the gas check shank missing.... These two bullets are "bore riders", and you can see the shiny spots on the nose of the 73 gr. where it rubbed along the lands.... The front driving band is engraved to about half the rifling depth, as it is sitting in about the middle of the leade.... There are very slight marks on the rear band from the back of the leade, and about the same on the back band of the Bowman (which is a copy of the Lyman 257420, scaled down to 6mm).... The middle band of the Bowman is engraved about half depth, and the very front of the front band is just about full rifling depth, which is what I aim for.... The 63 gr. barely touches the leade with the front band, but if you push slowly on it, you can feel that it is seated firmly against it, but just enough to leave tiny marks.... There are some tiny polished spots on the nose, just at the back of the ogive, where it is just sitting on the lands.... I'm very pleased with the way this chamber came out.... In terms of size, a bullet sized to 0.243" slides in easily.... but one sized to 0.244" requires a bit of a push.... so the chamber size is perfect.... This reamer is a KEEPER !!!
This afternoon I set up the receivers in my milling attachment in the lathe, and adjusted it so that it cut a 20 MOA angle into the top of the Dovetails.... That works out to only about 1mm (0.040") less height at the front of the dovetail than at the rear.... but should put the POI at about optical center of the scope at 100 yards.... I then machined the dovetails into the sides of the raised portions on the receivers.... I took a bunch of photos of the two receivers with the dovetails, and had trouble with reflections hiding the angle of the dovetails.... but you can just about see that in the photo below (with a little imagination)....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Angled%20Dovetails_zpsm5txavkk.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Angled%20Dovetails_zpsm5txavkk.jpg.html)
If you look closely, you will see that at the front of the dovetail, the bottom of the cutter ran along the top edge of the bevel on the corners of the receiver.... but at the back of the dovetail the cutter left a ridge 1mm above the top of the bevel.... It's hard to believe that is all the elevation angle required of the barrel, relative to the scope, to put you on target at 100 yards.... but 0.040" in 6" works out to 24" at 100 yards (0.040 x 100 x 3 x 12/6).... When you mount the scope you can barely see the angle, if you didn't know it was there you would never notice it....
Bob
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So, yep, about RC 60 would seem correct.... not that I have any real idea if that is the best for the job or not.... *LOL*....
That is over twice the likely hardness of the barrel; so, perfect. Besides, O1 has been used for a long time. It is almost on par with high speed steel; except that if you overheat O1 by cutting too fast (or fast and dry), the cutting edge hardness will be lost. The way you use your reamers, this is of no concern.
O1's beauty is that it is not expensive, and you can make your own tools. Now, I have played around with A2 tool steel because you don't have to quench it in oil or water to harden it, so it distorts less from thermal shock.
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double post...
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Barrel is 4130 CrMoly, probably started as normalized tubing, but who knows what the hardness is after hammer forging....
Bob
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Barrel is 4130 CrMoly, probably started as normalized tubing, but who knows what the hardness is after hammer forging....
Bob
Probably no more than 30 Rc at the surface. Less in the bulk, but more than before hammer forging.
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Over the last 3 days I machined the O-ring groove in the breech of both barrels, and cut the CF sleeve to length and glued it onto the barrel liner with Loctite 638 (green).... After curing 24 hours, I gave it a post-cure in my wife's oven at 175*F for 3 hours.... This greatly enhances the strength of the bond.... Today I laid out and machined the barrel ports, and then installed each barrel in its receiver with a couple of setscrews (just tightened a bit against the CF sleeve), making sure the flat on the barrel port was perfectly centered in the hole in the receiver for the transfer port.... I made a drill jig from a 20mm long x M5 SHCS by drilling a 1/8" hole through it in the lathe.... and then inserted it in each of the holes in turn and drilled through the carbon fibre until I touched the steel of the barrel with the 1/8" drill bit.... I then mounted the barrel in my milling attachment in the lathe, centering off each 1/8" pilot hole, and enlarged the hole to clear the M5 setscrews with a #8 drill.... I drilled deep enough to leave a shallow pocket in the steel liner for each screw.... Here is the way that works....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Drilling%20Jig%20and%20Barrel%20Port_zps81wbc9mu.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Drilling%20Jig%20and%20Barrel%20Port_zps81wbc9mu.jpg.html)
The piece of tape on the drill bit was just a visual indicator to let me know when I would hit the steel.... The drilled out M5 SHCS worked perfectly as a drill guide, it is a great way to mark setscrew pockets accurately in a barrel.... I deburred the barrel ports and faired the 0.260" round transfer port seat ID into the oblong barrel port which had been machined with a 3/16" end mill.... The port in the 6 mm ended up at 0.194" wide by 0.294" long and the one in the .257 is 0.205" wide by 0.305" long.... which gives me full bore-area porting in both barrels.... Here is a photo of one of the finished barrels installed in the receiver....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Barrel%20Installation_zpsenxjy7t0.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Barrel%20Installation_zpsenxjy7t0.jpg.html)
The next job is to complete the bolts.... I already have them turned down to diameter, but have yet to install the bolt handles and cut
them to length at both ends.... The barrels also need lapping inside with JB's Bore Paste and polishing with Bore Brite.... I'm getting pretty close to being able to take the first shots....
Bob
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Nifty!
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I can't wait to get started on mine!!!
All your work looks amazing Bob!
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Bob, I like that drill busing idea for a tapped hole. Very clever!
The build is looking great!
Lloyd
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Final assembly and first shots today.... Yesterday I cut the bolts to length and drilled and tapped them for the bolt handles.... I checked the chambering of all the bullets, and the .257 was OK but the longest 6mm bullet (73 gr.) was too hard to chamber, so I had to shorten the front of the bolt about 0.050" until I could just chamber it.... I then sanded the receivers and cleaned them thoroughly, inside and out.... Today I lapped the bores with JBs Bore Paste and then polished them with Bore Brite.... I made the bolt handles, and cleaned and assembled the uppers for the first time.... Everything worked smoothly, so I measured the required length for the transfer port on the unregulated gun (I'm still waiting for the regulator to finish the other lower).... It turns out the both the 6mm and .257 will require the same length transfer ports, which means I won't have to make multiples, just one for each lower.... The transfer ports are made from a piece of 3/8" OD Teflon rod, drilled out with a size "F" drill (0.257") and faced flat on the ends to the correct length to have about 0.020" of crush for sealing.... That was the last part required, so I was able to bolt the upper to the lower for the first time.... I put the .257 cal upper on the unregulated lower, and here is what it looks like.... The reservoir is 300 cc, and the gun as shown weighs 6 lb. 9 oz.... Using an aluminum reservoir sure makes a HUGE difference to the weight....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/257%20Unregulated_zps5wxd9klz.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/257%20Unregulated_zps5wxd9klz.jpg.html)
Well, the first shot is always an exciting and nervous time.... My Great White was at 3400 psi, so that was the fill pressure I used.... I sized some 82.5 gr. bullets, about in the middle of the weight range I hope to use, set up my Chrony and fired the first shot.... VERY loud, and 978 fps (175 FPE).... I increased the SSG gap from the 1 turn I had it set to, a turn at a time, and it made NO difference to the velocity, so I was firmly up on the plateau, and using a lot of air, the pressure in the Great White dropping a bit with each shot.... Suddenly I got a huge BRRAAAPPPPP which dropped the pressure about 100 psi.... I backed the SSG out a couple more turns, and it did the same thing.... after a couple more big burps, it was time to try something different.... I removed the SSG and set the preload on the 13 lb/in. spring to zero, and reinstalled it with 1 turn of gap.... by this time the pressure was down to just over 3000 psi, and I got a nice sharp report, still pretty loud, and 933 fps (160 FPE).... I started increasing the gap on the SSG, and the velocity stayed the same, but the gun was getting progressively quieter, but still using a lot of air.... Suddenly on one shot, all I got was a click.... Hammer hit the valve, but the gun did not fire.... I started cranking the SSG back in to increase the hammer strike, but even with zero gap, no joy.... I figured something inside the valve had failed, so I degassed the gun and pulled it all apart.... This is what I found....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Broken%20Valve_zpsa3kdn2zs.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Broken%20Valve_zpsa3kdn2zs.jpg.html)
The slotted wheel on the front end of the valve had sheared, and the sleeve over the poppet was no longer attached to the valve, but travelling with the poppet.... This meant there was no balancing force left on the poppet, so no wonder it would not open with the very light hammer strike.... If you ever need proof that the ART/SS valve reduces the required hammer strike, there it is.... I have tried to wrap my brain around where the force came from that sheared that wheel, and for the life of me, I can't see how there is any force on it, with the poppet free to slide inside it.... but there obviously is.... I am using a stepped poppet, with a 1/4" small end and a 3/8" big end, inside that sleeve, so the difference in those areas creates a balancing force of 184 lbs. at 3000 psi (258 lbs. at my 4200 psi MSWP).... If that force is "lifting" the poppet away from the seat to reduce the 464 lb. closing force (at 4200 psi) to "only" 206 lbs.... then I guess it must be "pulling" that sleeve downwards (towards the seat) with that same 258 lbs. of force (it has to go somewhere).... That was enough to shear the four very thin webs between the slots in the wheel that was holding it....
The first shots met or exceeded my expectations, but time for a redesign of that wheel.... ::)
Bob
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the numbers are simply INCREDIBLE! The gun looks awesome ,and quite utilitarian .. Question , is the tube 2024 or 7075 ?? I know its somewhere in the thread, I just don't recall. As for the valve, I read how you described the failure, I still cant see what started the chain of events. Sounds like a failed oring in the " balanced side " can cause a massive increase in load , enough to snap the web..
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Nice Bob!
Did I mention something about the end support strength to you or to Travis?
When making more power you need to consider the internal forces acting against the end on shot cycle. None the less awesome work on the guns.
Marko
Edit: Take the forces at play, and add the full hammer blow to that, followed by the BRRRAPPP and I dont wonder why the end failed. I'm betting the valve bottomed out pretty good on the first shot.
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The tube is 2024-T3 on both guns, but the one on the unregulated gun is 0.120" wall, so the MSWP is 4200 psi at a 3.5:1 safety margin.... The O-rings in the valve were 100% intact, there was NO leakage out the barrel either before or after the valve failed.... and they appear perfect on disassembly.... in fact the sleeve was still just sitting on the poppet like nothing had happened....
Marko, you did indeed warn me against using a snap-ring to retain that wheel, but if I understand what happened correctly, the force on the sleeve is inwards, towards the valve seat.... since the effect of the stepped poppet is to reduce the force in that direction.... equal and opposite, right?.... The wheel sits against a shoulder, the snap-ring simply retains it there.... The four thin vanes between the slots simply sheared off....
The poppet cannot be driven to the limit of it's travel by the hammer, because the hammer hits the end of the valve before the poppet runs out of travel.... In addition, poppets seldom open all the way anyways, and would not travel as far on a "bounce" as the initial strike.... I really doubt if the hammer bounce harmed the valve in any way, or was responsible for breaking the wheel.... It was many, many shots after I eliminated the bounce, and with a much lighter hammer strike, when the wheel broke.... I suppose it could have cracked during one of the BRRAAPPPPs.... but I know for sure the hammer cannot bottom out the poppet, I was very careful about that when I made the valve.... I think the 184 lbs. of load was just too much for the small amount of metal I left in between the slots....
Bob
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Man does that look failure. I dont have pics anymore but in the ART gate I had a SS 357 Bulldog valve that did almost the same thing so I had to beef it up also. If your getting the Brrraaapp the ratio is still under balanced and can use a closer ratio between 70-80% of diameter of the two pistons but this comes at a price of harder cocking of course. In the Bulldog SS valve it didnt shear it bent or mushroomed till the Thimble rested on the poppet making it impossible to open. The fun never stops with R&D but you have to admit theres always something to learn in our failures. The rifle looks really really awesome by the way.
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Found the pics. Failed thimble retainer and new thicker retainer that held.
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You'd be surprised how hard bigger balanced valve slams wide open. I have seen gouges on aluminum valve body for it hitting the balancer cylinder sleeve.
Marko
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Not trying to thread-jack, but I've changed my plans slightly for my 6mm build Bob.
I'm going to work with Jim at WAR to build a 6mm Flex. I've finally come to the realization that going this route will produce a better airgun than I can build. Plus I would have had to farm out most of the machining work anyway. I'll keep you posted Bob, just not on this thread... I want to keep this open for just your 6mm build.
Awesome work on your build so far Bob!! Sad about your valve... But you'll be back up and shooting soon, I have no doubt!!
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Travis, that photo of the failed retainer certainly proves that the force on the thimble is towards the valve seat.... *LOL*....
Bob
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Travis, that photo of the failed retainer certainly proves that the force on the thimble is towards the valve seat.... *LOL*....
Bob
Yes Sir the force has to go somewhere you dont get something for free right, every action has and equal and opposite reaction and that energy is throwing the thimble towards the seat.
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I had trouble wrapping my brain around the forces on the thimble, but I finally understood it (I think) by looking at what happens in the closed position, and considering the poppet as a fixed portion of the valve, and what the forces would be on the thimble if it were the part free floating.... Since the air pressure inside it is atmospheric, but all other areas of the valve are HPA, there is a net force on the thimble towards the seat of pressure times area.... the area is the area of the ID of the large part of the thimble minus the area of the small part.... In the case of my version of the ART/SS valve, that is a 3/8" bore (0.110 sq.in) minus a 1/4" bore (0.049 sq.in).... a total effective area of 0.061 sq.in.... At 4200 psi, that would be (0.061 x 4200) = 256 lbs.... quite a load on the tiny webs of aluminum I left in that wheel.... Well, time to hit the shop and make a stronger one....
Bob
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It seems that most of these "opportunities for improvement" never show up until you increase the pressure, or increase the power, or increase the caliber. Basically, they don't don't show up until we start getting greedy. But that is part of the fun, and it makes us stop, and think, and learn. Nice observations.
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Could you imagine a world without failure! How boring would that be!
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Could you imagine a world without failure! How boring would that be!
Absolutely! You would never learn anything new! Or dream up a solution to problem. A day without learning something new, is a day wasted. Even if its just that M&Ms have some new colors. ;D
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SUCCESS !!!
I made a new wheel to mount the front of the valve thimble, with eight 5/32" holes (a total area twice the valve throat), and with the center twice as thick and the webs between the hole more than twice as long, and twice as many of them.... I don't think I will have any more problems.... I put the gun back together and filled it, and my Great White is now down to about 2900 psi.... I installed the 6mm upper instead of the .257, using the same transfer port, and it sealed great.... I sized some of the 61.3 gr. Bowman bullets (a Lyman 257420, scaled down to 6 mm) to 0.243", and replaced the hammer spring with the weakest 3" long spring I have, one of 0.055" wire with a rate of 11 lb/in.... I set the preload to zero, the SSG gap to 1 turn, and shot the first 6 mm bullet.... It ripped through the Chrony at 1007 fps (138 FPE).... 8)
The gun was pretty loud, so I increased the SSG gap 2 turns as a time, recording the velocity as I went.... It didn't start to drop significantly until I was 7 turns out, and then it was still 990 fps.... I changed the gap only 1 turn at a time after that, recording the velocity until 14 turns out from zero gap, at which point it did not fire.... Turning it back in just one turn, the gun shot at 800 fps.... So, I had an adjustment range of about 200 fps before the valve fell off the cliff.... I now have a digital pressure gauge, so I put that in between my tank and the gun, so that I could measure the pressure drop per shot to determine the efficiency.... I started at 12 turns of gap (0.428"), filled the gun to the pressure remaining in the tank (2840 psi), closed the valve, let the pressure settle, and then fired one shot, let the pressure stabilze again and recorded the difference in pressure, and the velocity.... I reduced the gap a turn, and repeated the procedure, recording the velocity and pressure drop at each setting until I was back to 1 turn of gap.... Here are the results....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/6mm%20Plateau%202800_zpsicuylijh.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/6mm%20Plateau%202800_zpsicuylijh.jpg.html)
I can't believe how easy the digital gauge makes it to accurately measure the pressure drop for just one shot.... The hardest thing is to try and get the reading at the same temperature each time.... The gauge is soooooooo sensitive that after a shot (which cools the reservoir from expansion of the air during the shot), that you can watch the gauge rise slowly as the reservoir returns to room temperature.... The best way is after you close the tank valve, before the shot, wait a minute or so for the temperature to stabilize, record the starting pressure, take the shot, and then after the shot wait until the gauge has stopped going UP and record that as the end pressure.... and then subtract to get the drop.... From there, my spreadsheet calculates the FPE and FPE/CI, with the only two inputs needed the velocity and pressure drop....
The plateau, at 2800 psi (which is what I had left at the end of the testing), is basically 1000 fps, and the useful knee of the tuning curve runs from 7-12 turns of gap.... With this 61.3 gr. bullet, it looks like about 9 turns of gap (about 5/16") is the sweet spot, giving 960 fps (126 FPE) at an efficiency of 1.24 FPE/CI.... The pressure only drops 80 psi per shot on the 300 cc reservoir, so it will be about twice that on the 150 cc plenum of the regulated version.... That is only about a 6% drop, so I should be able to regulate at the 2800 psi I ran these tests at, at least with this bullet, maybe 100 psi less with the 58.3 gr HP version.... More testing will produce similar information for the other bullet weights I have, but first I have to refill my Great White.... I have a 3000 psi regulator I can tether to, it will be interesting to test the 73 gr. bullet at that pressure.... I will need to get a weaker hammer spring in order to reduce the SSG gap to a more reasonable 1/8" or so.... The cocking force the way the gun is tuned now is less than 8 lbs.... MAN, do these ART/SS valve ever work to reduce that, I'm VERY impressed, and happy with my first effort building one.... and only 2 failures along the way.... ::)
Bob
M&Ms have new colours?.... Count me IN !!!
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Bob,
Nice work on getting the broken part re-designed and built.
The gun looks nice and tunable, with good efficiency. Your graphing methods make finding the sweet spot pretty obvious and it sounds like the digital gauge makes that easier and more accurate.
This project is producing a versatile airgun package.
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With such light cocking one could easily vent shroud back pressure and make a semi auto(not in Canada). Just a few design changes. Bravo Bob you really out did yourself with this build.
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I put the numbers into the spreadsheet, and for the 960 fps (126 FPE) tune at 1.24 FPE/CI I have to put 87% in (M3) to balance it.... Dwell time is 0.0022 sec. and the valve closes when the bullet is 35% of the way down the bore.... I haven't actually kept track of that for my other guns, and of course the exponents for adiabatic or isothermal expansion, and when you use them, change it a lot.... but I don't remember having anything that high before.... I am using my standard conditions, isothermal when valve open and adiabatic when closed.... but now that I can observe the reservoir pressure (temperature) recovering after I shoot, I may change my opinion about that.... What do you think, Lloyd?.... Should we be using adiabatic all the time?.... Hmmmmmmm.... just answered my own question, I tried it, and had to use 1.05 in cell (M3), and 105% is impossible, of course.... ::)
In terms of my "lofty goal", this gun has full bore area porting, it is .243 cal, 29" barrel, and currently at 2800 psi, so the prediction is....
(0.243 x 0.243 x PI/4) x 2800 x (29 / 12 / 2) = 130 lbs. x 1.21 ft. = 157 FPE....
At the plateau I am getting 136 FPE with a 61.3 gr. bullet at 1000 fps.... It will be interesting to see what I get with the 73 gr. bullet....
Bob
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136 / 157 = 87% of the theoretically maximum FPE. That is pretty darn good, Bob! Especially, considering you are not wasting air.
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(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/257%20Unregulated_zps5wxd9klz.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/257%20Unregulated_zps5wxd9klz.jpg.html)
Bob
Amazing power, efficiency and also accuracy - I am sure , because the barrel is stiffening free floating and harmonic adjusted .
The design of guns is veeeery practical however higher scope rings will be needed.
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Well the 157 FPE is NOT the theoretical maximum FPE, that would be twice that.... My "lofty goal" numbers are already derated by 50% to allow for the weight of the air accelerated (the largest single loss, 31 gr. of air per shot at the current tune, 1/2 the bullet weight), drag on the bullet, and the fact there is a pressure drop during the shot because the reservoir is not infinite and there is wasted volume before the bullet in the porting system.... Using 50% s still a VERY hard goal to attain, if you are using a bullet that weighs 1/2 the FPE (ie at 950 fps).... although you can reach or exceed that number with a very heavy bullet.... In a dump shot (valve closes at the muzzle) there would be 77 gr. of air in the barrel when the bullet exits.... so you can see why a heavy bullet helps you achieve 50%.... while light bullets don't have much of a chance to get there....
Actually, medium height scope rings still have tons of clearance with the 44mm AO scope I have, and even more with the side focus one.... I don't think a 50mm objective would be a problem, even with the scope tilted down 22 MOA relative to the barrel....
Bob
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I had a slight leak, and the reservoir was empty this morning, so while I was filling my Great White this morning I pulled the gun apart and replaced all the O-rings.... Afterwards, I found there was still a slight leak through the valve.... Soapy water on a fingertip pressed to the end of the barrel (with the bolt closed) was met with a steady stream of small bubbles.... I don't know if it is the O-rings in the valve, or the poppet not seating perfectly, but after my tank was filled and I tethered it to my 3850 psi output regulator and fired it a few times the leak is almost gone.... I think with time and use, it may seal up OK.... I sized some of the 82.5 gr. bullets to 0.257", set the SSG gap to 1 turn and fired the first shot at this pressure.... 1010 fps for 187 FPE !!!
I followed the same procedure as yesterday with the 6 mm, gradually increasing the SSG gap until the valve quit opening, and recording the velocity at each setting.... Since the regulator was topping up the reservoir after each shot, I was unable to record the pressure drop to figure out the efficiency.... However, I did establish the tuning curve for the .257 when tethered at 3850 psi....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/257%20Plateau%203800_zpstzfmhqis.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/257%20Plateau%203800_zpstzfmhqis.jpg.html)
As you can see, with less than 5 turns of gap, the gun is operating on the plateau, just above 1000 fps.... The usable part of the knee is from 7-11 turns of SSG gap.... Surprisingly, the sweet spot was at 9 turns of gap, exactly the same as the 6 mm at 2800 psi.... I would have thought that the hammer strike required would have increased a lot with the 1000 psi increase in pressure (certainly in a conventional valve that is the case).... but it didn't, so one more thing I have learned about (my version) of the SS valve.... I then set the gap back to just 1 turn, to put the gun back to maximum power, and tried all the different bullet weights I have in .257 cal.... Here are those results at 3850 psi....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/257%20FPE%20at%203800_zpsnxzgi5re.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/257%20FPE%20at%203800_zpsnxzgi5re.jpg.html)
It was driving the 66 gr. 257420 HPs nearly at Mach 1 (VERY loud), and the 73 gr. 257420 solids at 1060 fps (182 FPE).... Bullets in the most likely weight range for this gun (82-93 gr.) were shooting 970-1010 fps (186-196 FPE), and the heaviest BBT I have, the 113 gr. FN, was able to reach 895 fps (201 FPE), with the 100 gr. BBT hitting 952 fps (201.3 FPE).... Drop about 4% off those velocities to allow for tuning down to where the efficiency is acceptable.... and I have a .257 shooting at 170-180 FPE.... This is about 20 FPE less than my Monocoque, which has a 5" longer barrel, at the same pressure.... My .257 Hayabusa, running the same barrel length but at only 3000 psi, peaked at 160 FPE and was tuned to shoot at 130-135 FPE.... If I want to tune this gun down to use the 257420s (FN or HP) all I need to do is regulate it to a lower pressure.... At the other end, I can drive my heaviest two BBTs fast enough to find out how they work in the 10" twist of this barrel.... so this gun will eventually prove invaluable for bullet testing.... exactly what I wanted.... With a MSWP of 4200 psi, I will be able to shoot the 113 gr. BBTs in the mid 900s....
I did one other test today.... After filling with the regulator to 3850 psi, I disconnected it from the tether and shot 3 shots, allowing the pressure to drop, just to see what happened.... I was back to using the 82.5 gr. bullets, and I had the SSG gap set back to 9 turns.... The velocities ran 952, 953, and 940 fps, averaging 165 FPE.... According to the small gauge on the side of the reservoir, the pressure dropped about 400 psi, which would indicate an efficiency of about 1.0 FPE/CI.... not a very accurate determination.... but shows me I am in the ballpark at that power....
Bob
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excellent numbers on such a small bore gun.. Do you think or know if the theoretical limits have been reached ? Ok , I think subscriber pointed out what I missed.
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Well the 157 FPE is NOT the theoretical maximum FPE, that would be twice that.... My "lofty goal" numbers are already derated by 50% to allow for the weight of the air accelerated...
Thanks. That makes perfect sense. I had not looked very hard at your calculations; so did not notice the 50% derating.
There seem to be a number of "natural limits" along 50% efficiency. Another would be the overall efficiency of diesel engines. The best ones only just get to 50%. These tend to be be large and very slow running; as used in ships and trains.
I have long thought of guns as "disposable piston engines"; so they would work along similar principles...
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Theoretical maximum FPE for .257 cal, 29" barrel, at 3850 psi is 482 FPE.... so my "lofty goal" would be half that, or 241 FPE, or more properly 950 fps with a 120 gr. bullet.... The bullet my gun shoots the closest to 950 fps is the 100 gr., which hit 201.3 FPE.... or 83.5% of the target.... Believe it or not, that isn't actually that good, the best PCPs hit about 90% of target when shooting a bullet at 950 fps.... If the barrel was 24", the "lofty goal" would have been 200 FPE.... It took me a 20% longer barrel to get there.... The 6 mm at 2800 psi came closer to its target FPE....
However, a 6.5 lb. .257 cal PCP that breaks 200 FPE is still a pretty pleasing accomplishment.... 8)
Bob
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Bob,
The power and air deficiency you are getting this early with your home designed and home made air rifle are very impressive; regardless of the numbers.
Now, to maximize power and efficiency even further, would you:
1. Go longer on the barrel; or
2. Keep the barrel length at about "100 calibers", but raise the operating pressure significantly? I recognize that HPA at over 4500 PSI is a very scarce animal.
3. Or does starting at a higher pressure not only enable longer barrels, but requires it; assuming the goal is very high power and efficiency?
Higher pressure air would be denser, so even a short barrel full would weigh a lot. However, the flow losses attributed to pushing air down the barrel would be reduced; or am I on the wrong track? Then again, am I correct to assume that the "viscosity"of air goes up at higher pressure too; or is this a negligible factor?
Do you have any idea what the "pellet" friction losses are? If you had an average pellet friction of 3 lb over 2 feet of barrel, that would be 6 ft.lbs, right?
Thanks
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Barrel length and pressure are the routes to increased FPE, assuming the caliber is a constant.... I am already at 120 calibers in the 6 mm and 113 calibers length in the .257.... My Monocoque .257 had an even longer barrel, 33", or 128 calibers, and had about 10% more FPE, peaking at 227 FPE at 4000 psi with the 113 gr. BBT at 950 fps.... When I tuned it for a shallow bell-curve starting at 3790 psi, I got 4 shots of 921, 935, 933, 924 ending at 3320 psi with the 109 gr. HP version, averaging 209 FPE at 1.04 FPE/CI.... That tune would allow me to shoot tethered at 3800 psi for as long as the SCBA tank stayed above that pressure....
Although 4500 psi will allow a further increase in FPE, you are indeed faced with how to fill the gun at that pressure, or keep it at that pressure tethered.... You could do that with a 6000 psi welding tank, but at 300 lbs. they are hardly portable like an SCBA tank is.... I don't think it is practical to tune a PCP for over 3800-4000 psi at the present time.... One other problem is that as you go above 3000 psi, Boyle's Law no longer works properly, because the gasses are not longer "ideal".... You have to start worrying about the VanDerWaals correction factor.... Density increases slower with pressure increase than Boyle would predict over 3000 psi in air.... That is the reason that a 4500 psi SCBA tank only holds 88 CF of air, not the 98 CF that Boyle would predict.... While that doesn't affect the FPE, it DOES affect the shot count.... You get about 30% fewer shots from 4500 psi down to 3000 than you do from 3000 down to 1500 if you are shooting a PCP tethered at 1500 psi....
I think your 3 lbs. drag over a 2 ft. barrel being 6 FPE of loss is about right.... I checked it with Lloyd's Internal Ballistics Spreadsheet and it seems to work out that way.... Starting drag is higher, but because it is only applied for a short distance has much less affect on the total losses....
Efficiency is closely related to where the pellet is in the barrel when the valve closes.... Closing the valve after the pellet leaves the muzzle only wastes air, of course, with no velocity gain.... What is harder to understand is that closing the valve when the pellet is 50% of the way down the bore saves half the air, but only drops the velocity about 3-5% from the maximum.... After that, closing the valve earlier starts to drop the velocity much quicker, but saves even more air.... Likewise, with a dump valve (one that dumps all the air inside on firing), using a valve volume greater than half the barrel volume gains little performance for the extra air used.... The smaller the dump valve (or the earlier you close the valve on a conventional PCP), the higher the efficiency.... Really high FPE/CI occurs with short dwell combined with heavy bullets.... All these factors interrelate in a complex way, but that is the Coles Notes version....
Bob
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Thanks for the education, Bob,
It sounds like for everyday PCPs, 3000 PSI is a very good pressure to operate from.
When it comes to regulated guns, I can see that you don't want the pressure set point too low. That a small plenum at higher pressure may be better than a large one at low pressure.
A large plenum would surely have a certain "lost volume": Similar to "scavenging losses" due to the space above the piston in an air compressor.
Certainly, because the peak force to drive the projectile is at the start, the regulated pressure needs to be well above that required to "break it loose, or some may stick in the breech. This may not be a factor with pellets, but with tight fitting slugs it might become a significant consideration.
Even if the whole plenum volume is "dumped", it may be easier to create the kind of pressure/distance curve you described for best efficiency, by means of a small plenum. That is, unless one can engineer a very well behaved valve system - as you seem to have achieved. Such a well behaved valve would seem to be imperative with an unregulated PCP.
Trying to understand the theory is one thing. Implementing it in a design, and then making it real by actually constructing your own guns, is at a whole other level. I have some experience with how much time and concentration it takes to machine parts on a manual lathe and mill (which is what I assume you are using). So, it is a pleasure to watch you produce these masterpieces. Even more so, because they work as you intended.
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Hmmmmmmm.... well there is a big difference between what we call a "plenum", which is a chamber holding the regulated air supply.... and a dump valve chamber, where all the air in the chamber is discharged on every shot, like what happens in a typical pumper.... If you are dumping all the air in the chamber/valve, then you don't want to go more than 1/2 the barrel volume, and smaller is a lot more efficient (but loses power).... Here is a chart that shows you what happens in that case.... Note that the 1/2 barrel volume rule of thumb applies regardless of pressure....
(http://i378.photobucket.com/albums/oo221/rsterne/Millenium%20Pumper/DumpValves_zps8ff30e30.jpg) (http://s378.photobucket.com/user/rsterne/media/Millenium%20Pumper/DumpValves_zps8ff30e30.jpg.html)
When you have a regulator between your main reservoir and the valve, since the regulator cannot even come close to topping up the valve in the 1-2 mSec. it is open.... you get a pressure drop in the valve during the shot cycle that is MUCH worse than before you installed the regulator, when the entire reservoir volume was available to keep the pressure up in the valve (assuming the valve inlet passages are larger than the outlet).... Here is an example of what happens as you change the plenum volume....
(http://i378.photobucket.com/albums/oo221/rsterne/PCP%20Internal%20Ballistics/MRodPlenum_zps845202ec.jpg) (http://s378.photobucket.com/user/rsterne/media/PCP%20Internal%20Ballistics/MRodPlenum_zps845202ec.jpg.html)
That chart is based on a .25 cal MRod that is shooting 45 FPE at an efficiency of 1 FPE/CI (which was typical a couple of years ago, before we all got on the efficiency bandwagon).... The red diamond shows what happens when instead of having the entire 215 cc reservoir available for the shot, you only have 45 cc.... where the plenum size is 1 cc per FPE.... You lose just over 2 FPE, or about 5%, because the smaller volume in the plenum causes a greater pressure drop at the valve seat.... The smaller you make the plenum, the greater the FPE loss, unless you increase the pressure to make up for it.... which in turn reduces the "headroom", or the difference between the fill pressure and the setpoint pressure.... and loses shot count.... Note in the chart that if the plenum was only 1/2 cc per FPE (23 cc), you have lost nearly 5 FPE or more than 10% of what you had at the same pressure.... You would have to increase the setpoint pressure 10% to make up for the loss in FPE....
As I said, that chart was before the big increase in efficiency we have seen in the past few years.... If the efficiency is higher, you use less air per FPE, so the pressure drop in the plenum is less.... That means that you can use a smaller plenum for the same power loss.... Many guns are modified by installing an "in-tube" regulator, where you lose reservoir volume from the space the regulator occupies, and any plenum you make (usually with a spacer between the regulator and valve).... In that type of installation, you have to come to a compromise on plenum volume, between making it bigger (with a lower setpoint but less reservoir) or making it smaller (with a higher setpoint with more reservoir).... There was a lot of discussion about this, and it seems that most have agreed that 1/2 cc per FPE is a good size to optimize shot count, even though it requires about a 10% higher setpoint than if the plenum was 1 cc per FPE....
When you have a separate bottle for a reservoir, as I will be using in the regulated 6 mm build, then your plenum volume is independent of the reservoir volume.... Therefore I designed this gun to use the 1 cc / FPE plenum size, because no matter what size I make it, I will still have 500 cc of 4500 psi air to feed it through the regulator.... In fact, the plenum will be about 150 cc, and the gun will only be shooting 120-140 FPE, so I am a little over what I "need" (although you can never be too big, IMO).... That is the advantage of using a reversed bottle under the main tube (which becomes the plenum).... finding space for a large enough plenum is no longer an issue.... and the bottle serves as the forestock....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/6mm%20Sporter_zpsoihmeiqp.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/6mm%20Sporter_zpsoihmeiqp.jpg.html)
Your comment about "scavenging losses" (if I understand you correctly) applies more to the "wasted volume" between the valve seat and the base of the pellet, which in Lloyd's spreadsheet we call the "Transfer Port Volume".... That volume should be kept as small as possible, because the air in the reservoir/plenum must expand to fill it before the pellet sees any pressure to start it on it's journey.... That process takes about 0.05 mSec if the distance is 1", because that is the average random molecular speed (1650 fps) of the air molecules.... If that "lost volume" is 5% of the plenum volume, you have lost 5% of the pressure before any force can be applied to the bullet.... On the other hand, you want the passages to be as large a diameter as possible to eliminate restrictions to the flow.... so another compromise....
I actually don't own a Mill, all I have is a milling attachment for my old Atlas 12 x 36 manual lathe.... The milling attachment has a very small vice (1" x 2.5") and a vertical travel of just over 3".... and the crossfeed on the carriage is just over 6".... so doing large parts is a challenge, and often requires accurate repositioning of the work.... However, with persistence, it is amazing just what can be accomplished if you have the time and patience....
One other thing.... you are 100% correct that a "well behaved valve" is critical for all PCPs, and is the key to power with efficiency....
Bob
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I spent the day today working on the forestock and BiPod mount for the unregulated gun.... The stock is a 10" long piece of 1-1/4" ABS plastic pipe.... It fits loosely over the main tube, and at the back fits under a notch in the receiver designed to clamp it in place against the top of the tube.... That leaves a gap at the bottom of just under 1/8".... At the front there is a curved, taperered shim inside the bottom of the tube, made from a piece of aluminum barstock.... It was quite complicated to machine, because the inside fits the 1.25" OD of the reservoir, and the outside fits the 1.36" ID of the plastic pipe.... and of course the two radii are offset.... I started with a short piece of 1.5"D bar stock, drilled a 1.25" hole 0.055" off center, then chucked it in the lathe and turned the outside down to fit inside the plastic pipe.... I ended up cutting over half the circle away, leaving a crescent shaped piece less than 1.25" wide by 1" long.... I took a short piece of Picatinny rail, milled a concave in the bottom to fit over the outside of the plastic pipe, then drilled and countersunk two holes in it for a pair of 6-32 SHCSs.... These went through two holes in the plastic pipe and were tapped into matching holes in the crescent, so the whole thing went together like a sandwich, with the plastic pipe the filling.... I had made the crescent just a bit too tight a fit, so a drum sander relieved it enough so that the complete forestock would slide over the main tube and back to fit into the notch in the front of the receiver.... Two setscrews tapped through the plastic pipe and crescent, one either side of the Picatinny rail, secure it against the reservoir, pulling it down tight against it, just like the receiver does at the rear.... It looks nice, and feel right, and is very solidly mounted.... I then attached the BiPod to the Picatinny rail, and mounted the scope my wife gave me for Christmas.... This is what the finished rifle looks like, complete with the Harmonic Tuner as well....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Completed%20257_zpsbzvp2ae6.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Completed%20257_zpsbzvp2ae6.jpg.html)
The scope is a BSA 4-14 x 44 Side Focus FFP on medium height Hawke mounts.... The gun as shown s 44.5" long, and weighs 9 lbs. 5 oz. and without the BiPod it is 8 lbs. 14 oz.... Without the Tuner, it would be 8 lbs. 6 oz.... and the bare rifle, as I said before, only 6 lbs. 9 oz....
Bob
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Thanks for taking the trouble to explain that, Bob.
The fact that you are using relatively primitive machines to make your airguns, makes this all the more impressive.
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looks incredible Bob..cant wait to see some long range results.
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Your comment about "scavenging losses" (if I understand you correctly) applies more to the "wasted volume" between the valve seat and the base of the pellet, which in Lloyd's spreadsheet we call the "Transfer Port Volume".... That volume should be kept as small as possible, because the air in the reservoir/plenum must expand to fill it before the pellet sees any pressure to start it on it's journey....
Not to belabor the point, Bob; but with a dump valve firing from a regulated plenum, the plenum volume would be added to the Transfer Port Volume. I am looking at it from not just the perspective of the pressure front meeting the pellet base in the chamber, but the whole pressure profile as the air in the barrel expands behind the pellet, all the way to the muzzle:
Simply put; the greater the expansion ratio, the better the efficiency: So, a small plenum "wins", assuming a dump valve. Now, you are using a sophisticated valve that acts very quickly; so perhaps what I am saying is irrelevant, rather than incorrect.
I key pointer to this seems to be: When using a plenum sized to .5 CC per FPE, that requires only 10% greater pressure to get the same performance as a plenum sized to achieve 1 CC per FPE.
Either that, or I am more confused than I thought :)
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looks incredible Bob..cant wait to see some long range results.
+1
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On almost all PCPs, only a small fraction of the air in the plenum is used during the shot, because the dwell of the valve is on the order of 1-2 mSec, while the bullet spends 2-4 mSec in the barrel.... If the valve is open for more than half the pellet travel in the barrel efficiency suffers bigtime.... I do not have a handle on the shortest dwell time usable (because there are too many varilables), and if you go too short (for example if the bullet has only moved 1% of the barrel length when the valve closes) the drag on the bullet will slow it down before it reaches the muzzle.... It is very common for the efficiency to peak when the valve is closing at 15-18% of the barrel length (a dwell of well under 1 mSec), and I have seen the efficiency still rising when the pellet has moved less than 10% of the barrel length (dwell of about 0.5 mSec)....
To understand what is happening to the pressure in a plenum where the valve is closing with the pellet only part way down the barrel, perhaps an example of what is happening to the pressure in the barrel would help.... Let's look at two examples, with a gun intended to shoot at 100 FPE, and having plenum volumes of 50 and 100 cc, both fed from a regulator at 2000 psi.... We will assume an efficiency of 1.0 FPE/CI, so the volume of air (in std. CI at atmospheric pressure) required is 100 CI.... At 2000 psi (138 bar) that 100 CI of air occupies (100 / 138) CI x 16.4 cc/CI = 11.9 cc.... so that is the volume of HPA required to create the 100 FPE shot....
For the 100 cc plenum.... Volume of HPA before shot = 100 cc.... The shot uses 11.9 cc, leaving (100 - 11.9) = 88.1 cc, which expands to fill the plenum, dropping the pressure to (88.1 / 100) x 2000 = 1762 psi.... so the average pressure during the shot was 1881 psi.... If you compare this to an infinite plenum, where there is no pressure drop, you will generate about 4% less FPE in the shot....
For the 50 cc plenum.... Pressure after the shot is (50 - 11.9) = 38.1 / 50 x 2000 = 1524 psi, and the average pressure is only 1762 psi.... about 12% less than with an infinitely large plenum..... Obviously, we would need to start with more than 2000 psi to get the same FPE as with the 100 cc plenum.... If we increase the pressure by the 10%, to 2200 psi, the pressure after the shot is now 1676 psi, and the average is 1938 psi, so the 50 cc plenum at 2200 would likely produce about 3% more FPE than would the 100 cc plenum at 2000.... However, if you were feeding these plenums from a fixed volume at 3000 psi, you would only have (3000 - 2200) = 800 psi of air supply, instead of 1000, yielding only 80% of the shot count....
I will include one more calculation, so that you can see what happens with a dump valve, which is still open when the pellet leaves the muzzle, where the valve volume is equal to the barrel volume.... Let's choose a barrel that I know can produce 100 FPE at 2000 psi, a .30 cal that is 24" long.... The barrel volume is (0.15^2 x PI x 24) = 1.7 CI = 28 cc.... so we will use the same volume (28cc) for the valve.... Starting with 2000 psi, and dumping all of it, the pressure when the bullet leaves the muzzle is 1000 psi (the volume has doubled from 28 cc to 56 cc at the instant the bullet reaches the muzzle).... Therefore, the average pressure for the shot is only 1500 psi.... To get back to the FPE of either of the above examples, we would need to increase the pressure to maybe 2500 psi, to get 1250 psi at the muzzle, and an average of 1875 psi.... Not only that, but since ALL the air in the valve was dumped, we actually used 28 cc of 2500 psi air to create our 100 FPE shot.... That works out to (28 / 16.4) x (2500 / 14.5) = 1.7 CI x 172 bar = 293 std. CI of air.... which drops the efficiency to (100 / 293) = 0.34 FPE/CI, or about a third the efficiency of the above examples.... This is exactly why dump valves are NOT the way to go for efficiency....
I hope the above examples help you to understand why larger plenum volumes increase the efficiency, because they have less pressure drop during the shot.... and also why dump valves are not used in PCPs, because they are so inefficient....
Bob
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Hi.
You say for a good eficiency to close the valve when the bullet is in middle of the barrel.
If the barrel is 24 inch long half of barrel is 12 inch . If we use a barrel with 12 inch length and close the valve near the muzle how much speed we can obtain? Dont mind eficiency.
It is hard to get 90 percent from 24 inch barrel speed ?
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You will get much less velocity and power with a 12" barrel, closing the valve at the muzzle, than you will with a 24" barrel, closing the valve when the pellet has only travelled 12".... This is because in the 24" barrel, you have all the air trapped in the first half of the barrel continuing to expand as the pellet travels through the second half, and it continues to add energy to the pellet that entire time....
As an example, if you have a .25 cal PCP shooting a 34 gr. pellet at 900 fps (60 FPE) from a 24" barrel, at 1.00 FPE/CI efficiency, with the valve closing at 12".... and you shorten the barrel to 12" (the valve still closing there) but make no other changes.... The velocity will drop to about 735 fps (41 FPE) while still using the same amount of air, so the efficiency drops to 0.68 FPE/CI.... With the 24"' barrel, the residual air pressure at the muzzle was 540 psi, but with the 12" barrel it is 1360 psi, so the report would be much louder as well.... The extra energy from the expanding air that gave you 900 fps in the 24" barrel now just gives you more noise and only 735 fps....
Actually, I stated that I would not use MORE dwell than that required to have the valve close with the pellet half way down the barrel, because the efficiency drops quickly when you do that.... Most of the time you want the valve to close when the pellet is only 20-35% of the way down the barrel....
Bob
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Thank you.
I understand now.
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I hope the above examples help you to understand why larger plenum volumes increase the efficiency, because they have less pressure drop during the shot.... and also why dump valves are not used in PCPs, because they are so inefficient....
Got it. Thanks
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Here is an additional chart that may interest you.... This is an output from Lloyd's Internal Ballistics Spreadsheet....
(http://i378.photobucket.com/albums/oo221/rsterne/PCP%20Internal%20Ballistics/Plenum%20Volume%201_zpsikpscy0e.jpg) (http://s378.photobucket.com/user/rsterne/media/PCP%20Internal%20Ballistics/Plenum%20Volume%201_zpsikpscy0e.jpg.html)
The pressure curves (pressure and velocity on the right axis) show clearly the point where the valve closes, I used the same dwell for all three plenum sizes, no other changes, just the plenum volume.... The gun was a Disco, tuned for 30 FPE with the full 135 cc reservoir on tap (FPE on the left axis).... With a 30 cc plenum that dropped to about 28 FPE, and with a 15 cc about 26 FPE.... Even though all shots started with 1800 psi, you can see that the pressure in the smaller plenums dropped more at valve opening, because of the wasted transfer port volume.... with the 15cc plenum already down by about 50 psi just to pressurize the space between valve seat and pellet.... After that, as the pellet moves down the barrel, and the air expands to fill that volume, the pressure drop is much more rapid with the smaller plenums.... When the valve closes, the pressure is about 1710 psi with the full 135 cc reservoir, about 1470 psi with the 30 cc, and only about 1250 psi with the 15 cc.... After the valve closes, the pressure drop is more rapid in all cases, as the air trapped between the valve and pellet expands to fill the barrel as it travels towards the muzzle.... Another interesting thing is that you can see what effect shortening the barrel would have on the velocity, energy and residual muzzle pressure (which shows up as report) with this modelling....
This spreadsheet is proprietary to Lloyd Sikes, and developed by him (with a bit of input from me).... The main variables are caliber, bullet weight, pressure, valve dwell, reservoir/plenum volume and barrel length.... There are additional losses calculated which are from including the air mass (the greatest loss) and you can choose air, Nitrogen or Helium.... transfer port (wasted) volume, bullet drag and starting friction, the type of expansion both valve closed and open (adiabatic, isothermal or in between), and lastly a "system efficiency factor" to make the results of the spreadsheet balance with empirical results for the gun in question.... Once you have all the "known" variables input, then you adjust the valve dwell and the system efficiency until both the velocity/FPE and the efficiency in FPE/CI match your test results.... There is only ONE combination of those two remaining variables that will match your testing, and the results are charted as above, plus tabulated.... Outputs include.... barrel volume, FPE/CI efficiency, air volume and pressure used per shot, muzzle velocity and FPE, bar-cc/FPE, bar-cc per shot, ending reservoir/plenum pressure, residual muzzle pressure, "lock time" (time bullet moves down barrel), % distance down barrel at valve close, % of muzzle velocity at that point, and grains of gas in the barrel at pellet exit.... It is continually evolving, future changes will include corrections to the air mass (and accelerations) due to the VanDerWaals effect (deviation from Boye's Law at very high pressures), and the effect of the smallest transfer port diameter.... The goal is to eventually get to the point that the system efficiency factor is close to 100%, by including all other losses in the calculations.... I don't think we will ever get there, but we are learning all the time, and improving the model as we go....
Bob
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Bob,
Very nice write up on the internal ballistics that you and I have been working on for ... golly, 7 years? Just shows how much you can do, even without any research grant money, LOL. The modeling is becoming more accurate with each major revision we make.
The VanDerWaals pressure modification that you suggested has proven difficult to incorporate, but it is important, and I am almost there. The modification for T-port dia should be a much easier change to make to the spreadsheet, and will have potentially greater impact.
This is one of those situations where we were probably 80% there in the first couple of years, but this last 20%has proven very challenging. But we will get there!
Lloyd
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Indeed we will.... and the journey itself has been worth it, IMO....
Bob
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Thanks, Bob.
I had to stare at that chart for two minutes for it to soak in. The density of profound information contained in it, had to overcome my own density :)
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All this information will someday be put into and app and allow the user to virtually build their gun down to the last FPE and CC. Now If I could just find someone who knows how to make apps.... ;D
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It just dawned on me that you or Lloyd could write a book on this stuff.
"Everything You Always Wanted To Know About Pellet Guns"
The theory, practical modifications, tuning, troubleshooting etc. Charts up the ying yang, pictures.
I have no idea how many would sell, but I'd buy one.
Or.... "Air Guns For Dummies"?
Steve
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Too much yet to do and learn to have time to write a book.... and I'll be 70 this year.... ::)
Bob
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Too much yet to do and learn to have time to write a book.... and I'll be 70 this year.... ::)
Bob
Fear not my septuagenarian friend your paving the way for others to follow in your foot steps. Hopefully the 20-30 year olds are putting all this knowledge away to use in future endeavors
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Too much yet to do and learn to have time to write a book.... and I'll be 70 this year.... ::)
Bob
Finally I have found out why you are much/cheerfully more clever than I . I am only 64.
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Too much yet to do and learn to have time to write a book.... and I'll be 70 this year.... ::)
Bob
Finally I have found out why you are much/cheerfully more clever than I . I am only 64.
Ha ha, remember when hitting 30, or 40, or even 50, was a big deal? Now, so long as we've got some semblance of good health, birthdays don't make a whole lot of difference. I am glad we are maturing nicely, rather than just getting over-ripe. :D
Lloyd
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sniff-sniff.... you SURE?.... :o
Bob
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I got the 18 mm x 1.5 mm regulator from Travis yesterday, and made a "tiny" tank from a piece of 1-1/8 steel roundbar 3" long, drilled 2" deep and tapped to match the regulator threads.... I already have one for 5/8"-18 NF threads, but this is the first time I needed one for a reg. with the larger threads.... I tested it the way it came, and it was set for 1,800 psi, and fitted with a 3K burst disc on the output side.... so I replaced the disc with a 5K because I need to be able to increase the pressure to as much as 3,200 psi, which is the MSWP for the tube on my regulated 6 mm.... From initial testing I wanted to try 2,800 psi, so I pulled the reg. apart and found some very strange looking Bellevilles.... Intead of a simple concave/convex shape, they were stamped with a ridge in them, halfway between the inside and outside edges.... Travis had sent me some standard 0.032" Bellevilles, which I am much more familiar with, so I decided to use those.... A series stack of the 0.032" thick would not allow me to get a high enough setpoint, and I would normally use the 0.047" ones for this pressure, but decided that since I had enough I would try a series/parallel arrangement using nested pairs of the 0.032" Bellevilles.... The data I had said that arrangement would be not quite as stiff as a single 0.047", which meant it should be easier to adjust.... I tried 6 pairs and got an output pressure of just 47 psi :o so I added another pair, a total or 14 of the 0.032" Bellevilles, arranged like this....
)) (( )) (( )) (( ))
The reg. body is on the left, and the large end of the piston is on the right.... This arrangement gave me about 2400 psi, and I tried a 0.020" shim and that jumped to 3300.... I ended up with 0.012" of shims and got a nice solid, stable 2800 psi, within about +- 10 psi each time I burped it.... and it returned to the setpoint pressure within a few seconds.... Although the base regulator is Chinese, it has a Delrin ball running on the seat, like the Ninja regs. do.... and seems very stable.... I guess I'll find out if it remains that way in the long term, but I have a good feeling about this combination.... I fitted it to my 500 cc 4500 psi CF bottle, measured up the length I needed to clear the trigger group, cut the tube to length, and set it up in my milling attachment in my lathe to drill the mounting holes for the tank block....
When I made the tank block, I put the holes at a 45 deg. angle to vertical/horizontal, so that I could remove it without pulling the barrel.... This made the setup to drill the holes so that the tank lined up with the trigger group a real PITA.... I ended up using a 5/16" steel rod through the valve screw holes, and a long level with a 45 deg. bubble, and checked and double-checked as I twisted the tube in the milling vice.... I positioned the milling attachment vice in the horizontal and vertical to drill the hole in the middle of the tube, and the correct distance from the end, and with much trepidation, drilled the first hole.... I deburred it while still in place, slid in the tank block and threaded in one screw, and the alignment looked good, so I drilled straight through the tube, and now had two holes.... I loosened the vice, turned the tube 90 deg., inserted the steel rod through them, and used a machinists square on the bed of the lathe to set the tube perfectly, and then checked the distance from the end, and drill the other two holes.... After deburring, all four screws went in with my fingers, and here is the result....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Tank%20Block%20Fitted_zpspnsypzz0.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Tank%20Block%20Fitted_zpspnsypzz0.jpg.html)
The next thing I have to do is build another set of "guts" for my version of the ART/SS valve.... Based on the results of the first one, I have more confidence in my ability to make a second one that will hopefully work "fresh off the lathe" compared to the long learning process I had the first time around.... Once the second valve is complete, I will be able to assemble the pressure tube and see if it holds air.... The tank / regulator assembly is currently sitting with 1500 psi in it and seems to be holding perfectly.... The plenum is exactly 11" long inside, which makes the volume including the valve 165 cc....
Bob
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Bob,
I haven't run into those ridged Bellvilles that you describe either. Do they possibly have some special attribute, like increased travel for the given thickness?
Its nice that the 7 pairs worked out so well. That should give plenty of adjustability. I've run into some cases where it was extremely difficult to find the right combo for a desired pressure. You go one way and it locks up, and you go the other way and the pressure totally drops. Looks like you have a winner.
You are using the 2024-T3 1.25dia x .095 wall tube for the plenum? Should work nice.
Lloyd
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Yes, the plenum for the regulated gun is 0.095" wall, the 0.120" wall I got from you is used in the unregulated (MSWP 4,200 psi).... I am using four 10-32 screws (installed like an MRod) in the valve and fill fitting on both guns.... Here is what those weird Chinese Bellevilles look like....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Stepped%20Bellevilles_zpscsw3sj7j.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Stepped%20Bellevilles_zpscsw3sj7j.jpg.html)
They are 0.022" thick material, and 0.046 tall.... I fished them out of the garbage to take a photo for you.... *LOL* .... The shims they used were smaller on the OD than the Bellevilles, I guess when they compress they bear on the edge between the outer rim and the angled part of the dish, with the outer edge picking up.... ie the effective OD gets smaller as they compress.... possibly giving a "progressive" rate?.... Maybe they built a better mousetrap and I chucked them.... ::)
I just looked up the specs on a 0.022" thick conventional Belleville, and using them stacked in pairs, the maximum pressure would only be about 1400 psi.... and this reg. did 1800 stock.... I'm guessing that means these kinked Bellevilles are stiffer for the same metal thickness, which makes sense.... progressive rate, I don't know.... I think they just act like they have a smaller OD....
Bob
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I spent yesterday making the "guts" for my SS valve.... I already had the body done, but this is a fiddly job, requiring accurate turning of the plastic poppet, including the O-ring grooves, spring seat and sealing face, plus drilling for the stem and vent.... and then making the matching thimble that it rides in from steel, and mounting it to the perforated wheel in the front of the valve.... In case you are wondering why I am not showing photographs of these parts, it is out of respect for Travis, who is applying for a patent on the design.... Anyways, I got it assembled last night, and had a slow leak out the exhaust port, which I cured today by taking another skim off the poppet sealing face and re-lapping it to the valve body.... After assembly with the 6mm upper, and a few test shots, it is now sitting for a leak-down test until tomorrow.... I used my "tiny" regulator test tank instead of the 500 cc CF bottle, so that I can drain the gun if it needs work without wasting all that HPA.... Once the gun is fully sorted, then I will simply unscrew the small steel "cylinder" from the regulator and spin the CF tank on in its place.... Here is what it looks like at the moment....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Regulated%20for%20Testing_zpsozzbopsf.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Regulated%20for%20Testing_zpsozzbopsf.jpg.html)
My digital gauge is on the inlet, just so I can keep check on the pressure.... I will tether the gun to my Great White for testing by connecting to the male Foster on the inlet of the gauge.... The regulator is set for 2800 psi, and this gun has not been tested before, previous testing was done on the 300 cc unregulated gun, whereas the plenum on this gun is just over half the size, at 165 cc including the valve volume.... I backed out the SSG gap until I saw a slight decrease in velocity, I would have gone further, but I don't have enough travel with the 11 lb/in spring, I will have to fit a weaker one.... I like to tune so that the velocity is 3-5% below the plateau to have decent efficiency.... I did find the plateau velocity with the three bullet weights I have, as follows....
61.3 gr. Bowman (257420 copy).... 993 fps (134 FPE)
63.8 gr. NOE 245-64 FN.... 971 fps (134 FPE)
73.4 gr. NOE 245-74 FN.... 913 fps (136 FPE)
I also have HP versions of all three, about 3 gr. lighter, which I did not test.... I am pleased that the velocity is very close to the same (within about 1%) with the smaller plenum, although it is over 1.2 cc per FPE so I did not expect a dramatic power loss.... It should be large enough to work fine on the .257 cal. upper as well, should I wish to shoot it on the regulated lower....
Now to get a weaker hammer spring so that I can tune this beast down a bit.... ::) 8)
Bob
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I spent yesterday making the "guts" for my SS valve.... I already had the body done, but this is a fiddly job, requiring accurate turning of the plastic poppet, including the O-ring grooves, spring seat and sealing face, plus drilling for the stem and vent.... and then making the matching thimble that it rides in from steel, and mounting it to the perforated wheel in the front of the valve.... In case you are wondering why I am not showing photographs of these parts, it is out of respect for Travis, who is applying for a patent on the design.... Anyways, I got it assembled last night, and had a slow leak out the exhaust port, which I cured today by taking another skim off the poppet sealing face and re-lapping it to the valve body.... After assembly with the 6mm upper, and a few test shots, it is now sitting for a leak-down test until tomorrow.... I used my "tiny" regulator test tank instead of the 500 cc CF bottle, so that I can drain the gun if it needs work without wasting all that HPA.... Once the gun is fully sorted, then I will simply unscrew the small steel "cylinder" from the regulator and spin the CF tank on in its place.... Here is what it looks like at the moment....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Regulated%20for%20Testing_zpsozzbopsf.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Regulated%20for%20Testing_zpsozzbopsf.jpg.html)
My digital gauge is on the inlet, just so I can keep check on the pressure.... I will tether the gun to my Great White for testing by connecting to the male Foster on the inlet of the gauge.... The regulator is set for 2800 psi, and this gun has not been tested before, previous testing was done on the 300 cc unregulated gun, whereas the plenum on this gun is just over half the size, at 165 cc including the valve volume.... I backed out the SSG gap until I saw a slight decrease in velocity, I would have gone further, but I don't have enough travel with the 11 lb/in spring, I will have to fit a weaker one.... I like to tune so that the velocity is 3-5% below the plateau to have decent efficiency.... I did find the plateau velocity with the three bullet weights I have, as follows....
61.3 gr. Bowman (257420 copy).... 993 fps (134 FPE)
63.8 gr. NOE 245-64 FN.... 971 fps (134 FPE)
73.4 gr. NOE 245-74 FN.... 913 fps (136 FPE)
I also have HP versions of all three, about 3 gr. lighter, which I did not test.... I am pleased that the velocity is very close to the same (within about 1%) with the smaller plenum, although it is over 1.2 cc per FPE so I did not expect a dramatic power loss.... It should be large enough to work fine on the .257 cal. upper as well, should I wish to shoot it on the regulated lower....
Now to get a weaker hammer spring so that I can tune this beast down a bit.... ::) 8)
Bob
Awesome job Bob.
A quick yes or no on the internals of your valve(I'll pm you why I asked this question). Are you using the exact internal as the current ART/SIKES VALVE for sale from Travis or is yours tweaked differently?
Peter
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Nope, not the same.... 1/4" small end, 3/8" big end, 3/8" poppet seal, 1/8" stem, 1/32" vent hole.... "floating" thimble of my own design (5/16" OD at the front, tapers up to 7/16" OD at the back), 1/16" hole in the front mounting screw where Travis uses a jet.... Designed it myself, loosely based on Lloyd's and Travis' prototype drawings....
Bob
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Nice work Bob,
Just out of curiosity what pressure do you hydro test your airtubes?
Or do you just relay on math?
Marko
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Bob,
The gun is coming together very nicely. Your careful pre-planning makes for less tweaking as it goes together, but I know there are still a lot of little things that get "improved" on the spot as the process continues.
Lloyd
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Marko, I don't have the facilities to Hydrotest, I just rely on the Math.... Fortunately, all the testing that Lloyd has done show that the math is, if anything slightly conservative.... in that testing to failure requires slightly more pressure than predicted.... and in every case the weakest link predicted by the math is the part that fails first....
Lloyd.... exactly why I don't make detailed drawings.... dimensions get changed "on the fly" as I make the parts.... to insure assembly goes as smoothly as possible (or is possible at all).... :o .... The "planning" and associated drawings is only to develop the concept and workability.... and find major problems before work begins.... ::)
Bob
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Are you using barlows equation or something else? I have used that with normal tensile stress area calculations for rough estimations and never had an unpredicted failure during hydro testing. Simulation is useful with complex shape objects so that is what I usually do first.
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Are you using barlows equation or something else? I have used that with normal tensile stress area calculations for rough estimations and never had an unpredicted failure during hydro testing. Simulation is useful with complex shape objects so that is what I usually do first.
We were using Barlow's equation for a long time until I started doing calculations for thick walled tubes for pressure testing fixtures. Barlow's formula, which is really just an approximation, is valid for thin walled tubes. I think thin walled is defined as the wall being no thicker than one twentieth of the diameter. But when the wall starts getting thicker than that, Barlows calculates the stress in the tube wall as being much higher than it really is, making it appear that a much thicker tube wall is required. I then switched to using the thickwalled formula , calculating the max stress in the tube wall, which is always at the I.D. of the tube wall.
Here are few examples of the hoop stress calculated using a couple of different formulas:
10,500 psi test pressure. .875 tube O.D. and .065 tube wall. Barlows using tube O.D. shows max stress of 70,673psi, Barlows using mean wall dia shows 65,423 psi max stress, and using the (not Barlows) Thick walled formula, max stress is 65,844psi.
That shows good correlation between the Barlows O.D. formula and the Thick walled calc.
But when you go to very high pressures and thick walls the correlation is poor.
30,000 psi test pressure. .625 tube O.D. and .156 tube wall. Barlows O.D. formula shows a max stress of 60,096 psi, Barlows mean wall diameter shows a stress of 45,096 psi, and the Thick Walled formula shows 50,085 psi.
So, my observation is that Barlows is fine for thinwalled tubes.
But for thick walled tubes, it is best to use the Thick Walled tube formula.
Barlows will cause you to over-design using the O.D. formula; Barlows will cause you to under-design if using the mean tube wall diameter (some people use the mean wall tube dia method); and if you use the thickwalled formula, you end up with a safe tube that is not over-designed.
Just my thoughts on the subject.
Lloyd
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and in case it's not clear.... I use the spreadsheet that Lloyd came up with for my reservoir design, as it includes calculations for the end plugs, either threaded or pinned with screws.... I use a design point of 3.5:1 to failure and 2.5:1 to yield on my builds....
Bob
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and in case it's not clear.... I use the spreadsheet that Lloyd came up with for my reservoir design, as it includes calculations for the end plugs, either threaded or pinned with screws.... I use a design point of 3.5:1 to failure and 2.5:1 to yield on my builds....
Bob
I must add that Bob and I have collaborated on this spreadsheet, along with a few other spreadsheets, adding refinements and features as time passed. All of the spreadsheets started out at a pretty basic level, but the enhancements are what made them more and more useful. Bob is often the one who suggests the enhancements, and after a few back and forth iterations between us, we end up with something that we are both happy with.
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Finn,
I am curious how you do your hydro testing, if Bob doesn't mind side-tracking the thread for a moment.
Thanks,
Lloyd
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I made a hand operated tester pump that goes to at least 600 bar (broken 500 bar gauge told me), pump is connected to the tested part via thin metal pipe and it goes through modified bucket lid. Water filled part is submerged in the bucket and the lid has thin glass tube attached to it. Everything is made watertight and air is bled from the bucket by injecting more water from bottom connector until it almost fills the glass tube. Pressure is built up and possible displacement measured by observing the water level in the glass tube. If the level does not drop after pressure release the part has yielded or something leaks. I dye the pressurized water to see if there was a leak and repeat the tests if needed. Some parts I measure with micrometer before and after. I don't intentionally use the setup for destructive testing.
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I have run into an interesting little hiccup with the regulated gun.... The new valve I made is as identical as I could to the old one.... It functions fine, and reaches the same plateau velocity at the same pressure, minus a few fps for the 165 cc plenum instead of the 300 cc reservoir.... However, it takes MUCH less hammer strike to reach the plateau, and it appears to have very little velocity adjustment range before hitting the cliff.... I am not 100% sure about the latter, because I cannot reduce the hammer strike to the point where the velocity drops much, and then one more turn (but right at the edge of my adjustment) it quits opening....
The only thing I noticed on disassembly is that the shiny mark on the poppet that should indicate where it is sealing is near the throat (5/16") instead of near the outer edge of the poppet (3/8"), where it was on the original valve.... Both surfaces were turned at 90 deg. to the axis of the valve, and have been lapped in.... The big end of the poppet is 3/8", the small end is 1/4".... with a 1/32" bleed hole to the exhaust port and a 1/16" "jet" in the front.... I know that the area of the seal on the poppet can affect how easy it opens, do you think that is what I am seeing.... If so, would cutting a thou or two of concavity in the poppet to force the seal to the outside edge prove that and cure it?....
Lloyd, what do you think?.... Travis?....
Bob
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Bob, Yes, the sealing "ring" being smaller than the large piston diameter is causing the situation.
If we have (at 2500 psi): sealing diameter= .375 dia(276lbs), large piston=.375 dia(276 lbs), small piston = .25 dia(123lbs), stem = .125 dia(31 lbs), return spring = 4 lbs
The cracking force with .375 seal dia is equal to: sealing dia -large piston + small piston + spring, = 276-276+123+4 = 127 lbs
The cracking force with .312 seal dia is equal to : 191-276+123+4 = 42lbs
Force to close for both situations is stem dia +spring = 31 lbs
That does indicate that you might be able to tune a misbehaving valve a little bit by adjusting the diameter where the poppet actually seats. It also shows that you are getting to the point where the valve might start to machine gun.
Lloyd
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........................ I don't intentionally use the setup for destructive testing.
Ha ha. I like that! ;)
Finn, thank you for that info. Do you test actual parts, but keep the stress below the yield point, or do you make an extra part and stress it higher? Or does it just depend on the situation?
Your testing sounds good, like scuba tank testing, which I think is usually done to 5/3 of the rated working pressure. Do you use air, oil, or water to pressurize the part? Just curious because it sounds like something I might want to set up for non-destructive testing.
Thanks, Lloyd.
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I have run into an interesting little hiccup with the regulated gun.... The new valve I made is as identical as I could to the old one.... It functions fine, and reaches the same plateau velocity at the same pressure, minus a few fps for the 165 cc plenum instead of the 300 cc reservoir.... However, it takes MUCH less hammer strike to reach the plateau, and it appears to have very little velocity adjustment range before hitting the cliff.... I am not 100% sure about the latter, because I cannot reduce the hammer strike to the point where the velocity drops much, and then one more turn (but right at the edge of my adjustment) it quits opening....
The only thing I noticed on disassembly is that the shiny mark on the poppet that should indicate where it is sealing is near the throat (5/16") instead of near the outer edge of the poppet (3/8"), where it was on the original valve.... Both surfaces were turned at 90 deg. to the axis of the valve, and have been lapped in.... The big end of the poppet is 3/8", the small end is 1/4".... with a 1/32" bleed hole to the exhaust port and a 1/16" "jet" in the front.... I know that the area of the seal on the poppet can affect how easy it opens, do you think that is what I am seeing.... If so, would cutting a thou or two of concavity in the poppet to force the seal to the outside edge prove that and cure it?....
Lloyd, what do you think?.... Travis?....
Bob
This is why I use a 75% of bore as my bare minimum your running 66% Our commercial units are at 80%to avoid low power tune issues but still easy cocking. 280 small end 350 big end=80% thats our commercial size
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Thanks, guys.... I will try making a very slight concave on the bottom of the poppet to force the sealing diameter to the outside edge.... That should make it act like the previous one....
I am still trying to wrap my head around why these valve require so little hammer strike.... There must be something going on after the poppet cracks off the seat, driving the valve open.... Since I am running effectively no jet (a 1/16" hole in the front) the only thing I can see causing the valve to "blow open" is the delay that the 1/32" vent through the poppet, from the exhaust port to the inner chamber, causes in the pressure in that chamber rising to HPA pressure.... Once that chamber reaches HPA pressure, the only closing force left is the stem diameter times the pressure, which we expect.... but if the chamber pressure lags the exhaust port pressure, during that lag time there is an opening force on the poppet, right?....
Bob
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Thanks, guys.... I will try making a very slight concave on the bottom of the poppet to force the sealing diameter to the outside edge.... That should make it act like the previous one....
I am still trying to wrap my head around why these valve require so little hammer strike.... There must be something going on after the poppet cracks off the seat, driving the valve open.... Since I am running effectively no jet (a 1/16" hole in the front) the only thing I can see causing the valve to "blow open" is the delay that the 1/32" vent through the poppet, from the exhaust port to the inner chamber, causes in the pressure in that chamber rising to HPA pressure.... Once that chamber reaches HPA pressure, the only closing force left is the stem diameter times the pressure, which we expect.... but if the chamber pressure lags the exhaust port pressure, during that lag time there is an opening force on the poppet, right?....
Bob
Bob I cant remember if it was you or Lloyd I was sharing data about the lifting force pushing up on the oring gland on the big piston.I have tons of data to support it.
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I can understand the 1/32" bleed hole possibly causing a delay on the refill of the piston chamber, especially if the hole is partially clogged or undersize. In the original prototype, I had about a .048 hole, which was too large, and the valve tried to close immediately after opening. It was very easy to open, but the refill rate was too fast and the valve did not want to stay open. I had to keep increasing the hammer strike to get any dwell from the valve. I finally threaded a thin wire thru the bleed hole and bent it a both ends to retain it, and that cut the refill rate back down and then the valve started behaving.
Travis, I remember you explaining about the lifting force, but honestly, I was never able to grasp what was happening. I am sure something is going on, I am just not picturing it yet. But I will try again. ;)
Lloyd
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I can understand the 1/32" bleed hole possibly causing a delay on the refill of the piston chamber, especially if the hole is partially clogged or undersize. In the original prototype, I had about a .048 hole, which was too large, and the valve tried to close immediately after opening. It was very easy to open, but the refill rate was too fast and the valve did not want to stay open. I had to keep increasing the hammer strike to get any dwell from the valve. I finally threaded a thin wire thru the bleed hole and bent it a both ends to retain it, and that cut the refill rate back down and then the valve started behaving.
Travis, I remember you explaining about the lifting force, but honestly, I was never able to grasp what was happening. I am sure something is going on, I am just not picturing it yet. But I will try again. ;)
Lloyd
If we take the data of the area of the small end piston then we can figure out the closing force applied to the large piston to the seat and there fore figure how much spring and hammer energy needed to unseat the poppet correct. Except it doesnt calculate and the energy needed is half that in my case that is with a 280/350 poppets. So remember the poppet I made with no small end and it had and oring rod going threw the fixture and out threw another oring at the fill end as it would be on a mrod to atmosphere. I couldnt hold the valve closed with my body weight when filling the tube the oring under the large poppet was lifting the piston. Ill find the pics I sent I have them on my shop lap top.
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Travis, I think i remember about those pictures now; you texted them to me and I wasn't able to open them. A question about that test set-up: was the poppet sealing at its extreme O.D., or was it sealing at the throat I.D., similar to what Bob is seeing?
Lloyd
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280 throat and 350 poppet setting on a flat base no raised lip
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I really have to restrict myself to one change at a time.... ::)
I took the valve apart today and drilled the vent in the poppet out to 0.040" (from 0.032") and undercut the seat on the poppet to move the sealing edge back out to the outside edge, like on the other valve.... Well, the gun is back to requiring the same SSG gap with the lightest bullets as before, instead of less hammer strike when the seal was further in, on the edge of the throar.... and I attribute that to moving the seat out to where it should be.... However, as I increase the bullet weight I seem to have lost velocity, and more hammer strike is required to hit the plateau.... I didn't do a lot of testing, because the valve is leaking slowly out through the barrel, which I think is the seat leaking again.... I'm not 100% sure, but I think the larger vent hole through the poppet, which in theory should not blow open the valve (as quickly) because the pressure inside the balance chamber should be rising quicker.... is doing that with the heavier bullets, but little change with the lightest one....
The more I work on this valve, the more confused I become.... :(
Bob
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Bob I went down that road and spent the better part of a month trying to find out how why what and where. It boils down to changing jets for different tunes and getting the correct ratio of the twin poppets. The Ratio is so important it really makes the whole tuning thing easier and has a wider spectrum. Ill suggest you up the % to at least 70% but I personally would go higher. Yes it will require more spring energy but its still a huge reduction from what a standard valve will do. JMHO
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Bob, while it didn't seem like much you just increased the surface are of the hole some 50% from the original, for me that is a big change.
Marko
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Yes, Marko, that was what I intended, to bring the area of the poppet seat back up to what is was on the first valve I built, which functioned well.... The second one, when sealing at the OD of the 5/16" throat, was so easy to open I could not get a light enough hammer strike with the original spring that worked with the first valve in the other gun.... The change to seating around the outside edge of the 3/8" poppet brought it back into a range that I can adjust.... That part of the change worked.... but of the two vent holes (0.032"" and 0.040") the smaller one seemed to have less hammer strike change when you changed bullet weight....
Travis, I know you have changed to a much larger small piston, and then are using the jets for "tuning".... but I need to wrap my brain around WHY the various changes work, and not just accept that they do.... I know this will be a painful process, but I just can't do something without knowing why I'm doing it.... especially when some of the changes are counter-intuitive to me.... I know you are trying to help, and believe me, I greatly appreciate it.... but I think this is a process I may just have to go through, as painful as it is....
Bob
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I was referring to change from .03 to .04 on the poppet port
Marko
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................................ but I need to wrap my brain around WHY the various changes work, and not just accept that they do.... I know this will be a painful process, but I just can't do something without knowing why I'm doing it.... especially when some of the changes are counter-intuitive to me................................................. but I think this is a process I may just have to go through, as painful as it is....
Bob
+1
Bob,
I TOTALLY understand. :'( Very well said!
Lloyd
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Ahhh, OK, Marko.... now I understand.... Yes, I agree, that is a large change in the vent, from 0.032 to 0.040".... about 56% more area.... but it was the smallest increment I had in drills larger than 1/32".... I can now go up in smaller increments, using numbered drills getting larger from #60.... there are 3 sizes between that and 3/64" (0.047").... The 3/64" is 2.25 times more area than the 1/32" (and 38% more than the 0.040"), and I probably can't go much larger than that without hitting the bottom of the large O-ring groove in the poppet.... I think that large changes (eg. 56% and then 125%, from 0.032" to 0.040" to 0.047") may tell us what we need to know, at least I hope so....
Lloyd and I both feel that if the vent was large enough, the pressure rise in the balance chamber would rise to nearly HPA pressure very quickly, maybe before the pellet even moves, leaving the major closing force at that point in the cycle just the stem area times the pressure (like in a conventional valve).... The smaller the vent hole through the poppet, the slower the pressure rise in the balance chamber, and the greater the tendency for the poppet to "blow open".... As you know, if the balance chamber stayed at atmospheric pressure, the valve (once cracked) would blow open, and stay open, until the reservoir was empty....
As it stands, the reduction in hammer strike for a given velocity/energy in the shot is actually much greater than required.... It is difficult to reduce the hammer strike enough, and when the valve blows open (like the Cothran), it begins to operate like a switch, either on or off (open or closed), which is what causes the "cliff" instead of a plateau/knee/downslope like a conventional valve, which makes it easy to tune to a bell curve, or for efficient regulated operation.... Travis has increased the diameter of the small piston to make the valve more tunable, and then fine tunes that with his jet.... While this process obviously works, it seems to me to be using a bandage to hold a splint to a broken leg, instead of not breaking the leg in the first place.... and believe me, I am NOT trying to be insulting to his solution.... I just think that with a better understanding of WHY these valves operate in the fashion they do, we can simplify them, broaden their range, and ease their tuning.... as least that is my hope....
My Dad always used to say "the man who knows how will always be found working for the man who knows why".... words of wisdom I have never forgotten, right up there with his other favourites...."the difficult we do immediately, the impossible takes slightly longer".... or the dreaded "you mean it CAN'T be done?" (immediately followed by him doing it, of course).... ::)
Bob
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OK, today I actually made some progress instead of going backwards.... I think.... ;D
I pulled the valve out of the regulated gun yet again, and drilled the vent hole in the poppet out to 3/64" (0.047").... This is now 50% larger than I started with, which means the area is 2.25 times as large.... The idea is to get the balance chamber to fill from the exhaust port the instant the poppet cracks off the seat, hopefully before the pellet even starts to move down the barrel.... This should prevent (or at least reduce) the valve's tendency to "blow open" the instant it is cracked, which I am pretty sure is the reason for the "cliff" on this and the Cothran valve.... While the Cothran has virtually no velocity adjustment between the plateau and falling over the cliff, the ART/SS valve has a pretty fair velocity adjustment range where you can reduce the velocity, and improve the efficiency, before the valve stops cycling properly, and the velocity plummets over the cliff....
The first tests with this valve (compared to the first valve I made which is in the unregulated gun) had a narrow adjustment range, and required even less hammer strike than the first valve, in fact so light I could barely back the hammer strike down to find the cliff.... I took it apart and drilled the vent hole out to 0.040" and made a slight concave in the poppet seat to move the seal back out to the outside edge, and got back to where the first valve was, with a bit more hammer strike required (the larger vent), and a similar adjustment range between the plateau and cliff.... but the valve was leaking and had to come apart again.... I drilled the vent out even bigger, to 0.047", and it looks like I fixed the leak.... The result is that it took more hammer strike to get the same velocity, although still wayyyyyyyyyyy less than a conventional valve with a 5/16" throat at 2800 psi would require.... What I also got, just as I had hoped for, was a MUCH larger adjustment range between the velocity and where the valve stopped functioning.... In fact the cliff has basically disappeared.... 8) .... I can adjust the velocity down to under 500 fps by just increasing the SSG gap, something I have NEVER seen before with my version of the ART/SS valve....
All is not perfect, however, because as you increase the hammer strike, and the velocity approaches the plateau, I go through a period of severe hammer bounce.... not a machine-gun but a real BUURRPPP.... and then as the SSG gap gets very small the hammer bounce disappears, probably because the valve is open until the bullet leaves the muzzle (gun is really loud and kicks) which is dropping the pressure in the exhaust port and not slamming the valve closed as hard.... I had been running no preload on the spring on the SSG, which isn't great for resisting hammer bounce, so I added 2 lbs. of preload, and then 4 lbs., and the period of hammer bounce got less each time, but of course I had to increase the SSG gap to get off the plateau and back to the adjustable portion of the curve.... Instead of running about 9 turns of gap (with no preload), I am running about 12 turns (with 4 lbs. preload).... However, I am delighted with the wide velocity adjustment range, so I think I'm on the right track, and the gun is still VERY easy to cock....
One of the cures for hammer bounce is a light hammer, of course, and it works well on a gun where you have lots of hammer strike available (without excess cocking force).... In a gun with an SSG, it generally reduces the gap because of the drastic reduction in hammer momentum, which allows more lift and less dwell.... The plan is to make a MUCH lighter hammer, I think I will try one with no metal core at all, just straight MDS.... May as well start there and back up if I have to.... ::)
Bob
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What size pilot hole is in the thimble?
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Still a 1/16" hole in the front of the thimble.... You said going larger makes no difference, right?.... I am trying to achieve "instant" venting at both ends.... The lack of any cliff is VERY encouraging, I have never seen a balanced valve without one before.... My aim is to have a valve that tunes like a conventional one, but with less hammer strike.... but I have no need to make it feather light, as long as it is reasonable....
Bob
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Still a 1/16" hole in the front of the thimble.... You said going larger makes no difference, right?.... I am trying to achieve "instant" venting at both ends.... The lack of any cliff is VERY encouraging, I have never seen a balanced valve without one before.... My aim is to have a valve that tunes like a conventional one, but with less hammer strike.... but I have no need to make it feather light, as long as it is reasonable....
Bob
Do you have any smaller drill sizes? Or can you thread it and make your own jet? 4mm etc. thread
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The "jet" is just an 8-32 pan head screw with a hole drilled through it.... I can make any size I want up to 3/32".... I have number drills down to #60 (0.040"), below that I only have 1/32" (0.032") or 1/64" (0.016") but I'm pretty sure that tiny a drill would just break in a steel screw....
Have you ever got your velocity below 500 fps on a bullet where the plateau is over 900 without hitting a cliff (50% adjustment range) ?....
Bob
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The "jet" is just an 8-32 pan head screw with a hole drilled through it.... I can make any size I want up to 3/32".... I have number drills down to #60 (0.040"), below that I only have 1/32" (0.032") or 1/64" (0.016") but I'm pretty sure that tiny a drill would just break in a steel screw....
Have you ever got your velocity below 500 fps on a bullet where the plateau is over 900 without hitting a cliff (50% adjustment range) ?....
Bob
yes but my piston ratio is higher. You can extend that range and efficiency also by making the pilot hole smaller its to large for your ratio. I would start around .040 this will require a slightly harder hammer strike but your so light now it would probably be a blessing. Bob is it hard to get to your pilot jet?
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I just have to pull the valve and make a new one by drilling an 8-32 screw.... If the light hammer doesn't give me what I want (which I can test without pulling the valve).... then I will try a smaller jet.... A 0.040" hole is only 40% of the area I have now at 1/16".... The last change to the 3/64" vent hole makes it 2.25 times more area than the original 1/32" vent....
While stellar efficiency would be nice, my primary concerns in order are: power, reasonable cocking effort, and then efficiency.... If I can get around 130 FPE with the 6mm at 2800 psi at 1.00 FPE/CI, I would have reached my baseline goal, that should give me about 25 shots on a 4500 psi fill.... Higher efficiency (ie more shots) is a big bonus, of course....
I am still in awe of the easy cocking this valve makes possible.... Are you using a 1/32" vent through the poppet?....
Bob
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I just have to pull the valve and make a new one by drilling an 8-32 screw.... If the light hammer doesn't give me what I want (which I can test without pulling the valve).... then I will try a smaller jet.... A 0.040" hole is only 40% of the area I have now at 1/16".... The last change to the 3/64" vent hole makes it 2.25 times more area than the original 1/32" vent....
While stellar efficiency would be nice, my primary concerns in order are: power, reasonable cocking effort, and then efficiency.... If I can get around 130 FPE with the 6mm at 2800 psi at 1.00 FPE/CI, I would have reached my baseline goal, that should give me about 25 shots on a 4500 psi fill.... Higher efficiency (ie more shots) is a big bonus, of course....
I am still in awe of the easy cocking this valve makes possible.... Are you using a 1/32" vent through the poppet?....
Bob
No but again our piston ratios are different but having been where you are now I know the smaller pilot jet will work wonders. Can you make your jet removable so you dont have to keep pulling the valve? Slot the top so a long screwdriver can reach down and unscrew it. I cant emphasize how much the smaller jet will help but it may take a few trys to get it perfect thats why I would start at .040 then go up if necessary. The one thing you havent played with is the pilot jet and it really is dramatic when its right.
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The screw also holds the thimble in place in the mounting wheel (a loose fit, so the thimble can self-align but without end play).... but once I am that far into disassembly it's not that hard to pull the valve.... and on the unregulated gun it would have to be a L O N G screwdriver indeed.... *LOL*....
Please let me know (via PM if necessary) the size vent hole you are using through the poppet....
Bob
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It depends on the power level but I typically use a .87 mm jet the reason I believe yours needs to be smaller is your ratio is lower there fore less stable and what I mean by that is a standard valve is what I call 100% stable as it has no tendency to blow open under almost any pressure and the further you are from 1/1 ratio the further unstable the valve gets. After many attempts and months of testing I found a 80% of bore between poppets to be ideal for most guns. 75% is good for easier opening but still stable enough to not blow open or go bbbbrrraaappp. Anything less than 75% was unstable to the point one couldn’t put pre-load on the poppet. So your around 66% and I’m amazed you could get it to seal to be honest with such low holding pressure. So with that low of a % I would increase the bleed like you did into balance chamber to control dwell and also decrease pilot to increase hammer energy needed and also increase lock time or shorten dwell. Your pretty skilled to be able to make this valve in shop it’s not easy even on a C&C. The other benefit will be a wider tuning spectrum.
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I wasn't concerned about using the 1/4" small end, since Lloyd's prototype used just 3/16", and the MRod valve I got from you, which works just fine, is 1/4".... It wasn't the jet size I was asking, but the "bleed hole" as you call it, that equalizes the pressure between the exhaust port / throat and the balance chamber.... I started at 1/32", went to 0.040", and I'm now at 3/64" (0.047") and the adjustment range is WAY better with the bigger vent / bleed hole.... I'm convinced that the bigger that hole, the faster the pressure builds in the balance chamber, and the more the valve acts like a conventional valve (with no blowing open).... I don't care about not being able to put preload on the poppet, as I want to run an SSG.... so my requirements are less stringent than yours, where you have to worry about people doing things the valve is not designed for....
The valve, IMO, operates best with an SSG with gap, and since I can easily get to the plateau velocity with a small gap, and have to run a big one to get into the more efficient operating range.... there is absolutely no danger of preload and run-away operation.... Now that I have it operating like a conventional valve in terms of tuning.... it is only a matter of finding the right combination of hammer strike, pressure, and possibly vent and jet sizes to optimize it.... There IS a light at the end of the tunnel, and I'm pretty sure now it's not the headlamp of an oncoming train.... :o
Bob
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I wasn't concerned about using the 1/4" small end, since Lloyd's prototype used just 3/16", and the MRod valve I got from you, which works just fine, is 1/4".... It wasn't the jet size I was asking, but the "bleed hole" as you call it, that equalizes the pressure between the exhaust port / throat and the balance chamber.... I started at 1/32", went to 0.040", and I'm now at 3/64" (0.047") and the adjustment range is WAY better with the bigger vent / bleed hole.... I'm convinced that the bigger that hole, the faster the pressure builds in the balance chamber, and the more the valve acts like a conventional valve (with no blowing open).... I don't care about not being able to put preload on the poppet, as I want to run an SSG.... so my requirements are less stringent than yours, where you have to worry about people doing things the valve is not designed for....
I use a .030 and let the pilot jet fine tune it the rest of the way if you use a big pressure orifice it will limit what you can do with the jet and I have found the best efficiency is to try and run as small a jet as your power level will allow. I know I keep hounding you to try it but when you do you’ll see. That thimble jet will have more effect than the bleed hole and it’s reversable.
The valve, IMO, operates best with an SSG with gap, and since I can easily get to the plateau velocity with a small gap, and have to run a big one to get into the more efficient operating range.... there is absolutely no danger of preload and run-away operation.... Now that I have it operating like a conventional valve in terms of tuning.... it is only a matter of finding the right combination of hammer strike, pressure, and possibly vent and jet sizes to optimize it.... There IS a light at the end of the tunnel, and I'm pretty sure now it's not the headlamp of an oncoming train.... :o
Bob
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Remember what I said about two steps forward, one step back?.... Well the all MDS hammer I made is too light to deliver maximum power with the valve with the 0.047" vent through the poppet.... Even with putting in a 14 lb/in spring, at 5 lbs. preload and zero gap on the SSG, I can't quite reach the plateau with the 61 gr. bullets, and I'm down about 10% on velocity (20% in FPE) with the 74 gr.... The good thing is that the shot cycle is a nice clean SNAP (although a loud one), with NO sign of hammer bounce.... However, the large vent, which is intended to make the valve more conventional in operation by eliminating (or reducing) the "blow-open" cycle is doing exactly that.... Basically the valve is operating like a conventional valve that is easier to crack, but that's all....
I have no doubt that by making a hammer that is in between the 32 grams I have now and the 59 grams I had before (both with the 11 gram cocking handle installed) I could find, somewhere, the perfect combination.... However, although not uncomfortable by any means, the cocking force is WAY greater with the light hammer, so I think I have gone too far on the (hard to change) vent size.... Before I pull the valve and make more changes, I am going to make an MDS hammer for the unregulated gun, which is working great except for having too large a gap in the SSG (about 5/16").... The valve in that gun has the original 0.032" vent through the poppet, so has a tendency to "blow open" but it looks like a lighter hammer will drastically reduce that tendency, so it may turn out that a light hammer with the small vent is the perfect combination....
It certainly makes sense to try that before deciding how to proceed with another round of changes on the valve in the regulated gun.... especially because changing out the hammer doesn't even require degassing the gun....
Bob
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Or open the thimble jet up a tad and that should get you back up on the knee
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The thimble jet is the same as always, 0.063", I haven't yet tried smaller.... HOWEVER, check this out....
I made an MDS hammer for the .257 unregulated gun, and it works perfectly.... I was able to run a bit of preload on the 11 lb/in spring and reduce the SSG gap.... and every shot was crisp with no hammer bounce.... and I was able to push the gun right up to 185-190 FPE at 3800 psi, which is more than I would ever run it because it would use too much air at that power.... I backed the power down to 950 fps with the 82.5 gr. bullet (165 FPE) and ended up with 1 lb. of preload and 8 turns of gap on the SSG, which gives me a cocking force of just 9 lbs.... If I go to the 100 gr. bullet I need to reduce the gap a couple of turns, and if I drop back to the 73.4 gr. 257420 I have to increase the gap a couple of turns to keep it under 1000 fps.... Between the easy preload adjustment and gap adjustment, I can tune the gun from a "mild" 130 FPE up to about 180 FPE before it becomes an air hog....
With the gun set for the 82.5 gr. bullets I filled it to 3850 psi (all the pressure that was in my tank), with my digital gauge connected to the gun, shut off the tank and drained the inlet side of the gauge (it has a check valve for that purpose) and shot a 5-shot string as follows....
953
948
947
935
911
The ending pressure was 3350 psi (it used exactly 100 psi per shot from the 300 cc reservoir), and the first 4 shots were within a 2% ES.... I know that at 4000 psi at this setting the velocity is slightly lower, so I will have 5-6 shots within a 2% ES when off tether with a 4K fill.... and of course tons of shot when tethered to the regulator within a few fps of 950.... The 500 psi pressure drop over the 5 shots averaging 939 fps (162 FPE) works out to an excellent 1.28 FPE/CI, which I am more than pleased with at that power with a .257....
The combination of my version of the ART/SS valve and the lightweight MDS hammer is a real winner.... The gun is easy to cock, has tons of power, and when dialed back about 5% below the maximum is also very efficient.... I am sure setting the power lower would get VERY impressive efficiency numbers, but what's the point, this is a long range Varmint gun.... This valve has the original 1/32" vent through the poppet, which I am now confident is a better choice than the 3/64" I tried in the regulated gun.... Something in between, like the 0.040" vent I tried briefly, would increase the hammer strike, but now that I know the original setup works well when used with an MDS hammer I think I will just stay with the 1/32" vent.... I would like to get a couple of 8 lb/in hammer springs and run them with more preload, so that I can reduce the SSG gap a bit more.... but for now this setup will more than do the job....
Bob
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Most excellent!!! So many ways to skin the cat as they say. Thats not much spring force to pop open a 4k fill thats for sure. This should really reach out well to those critters WAY out there. Better start looking for a bigger scope.
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My Monocoque .257, operating at the same pressure, had a 182 gr. hammer with 1.4" of travel, and took 21 lbs. to cock it.... ::)
Bob
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My Monocoque .257, operating at the same pressure, had a 182 gr. hammer with 1.4" of travel, and took 21 lbs. to cock it.... ::)
Bob
Thats a crazy heavy hammer and a VERY stiff spring but thats what it took before balanced valves made their way into our lives. Two years ago we were banging highly sprung steel weights into thin valve stems now a mere 2 years later were using forces a low powered 22 would use to operate. Two years from now?????
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That is crazy heavy hammer and spring, I have not used that heavy hammer on any of my guns. Savage hammer was around 145gr at 800fpe. Did use 50mm of travel though.
In two years we will be using micro switch type bleed valves to actuate pneumatic actions to cycle the guns. ;)
Marko
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My .457 Hayabusa uses a 237 gr. hammer with 2" (50 mm) of travel to get 550 FPE.... Cocking force is 32 lbs.... I can just get to the plateau (maximum velocity) at 3600 psi.... I think just maybe it is a candidate for a (larger) SS Valve.... the throat is currently 0.406", but I would go to 7/16" (0.437") and enlarge the ports.... I would not have been able to max. that out with a conventional valve.... You can open the valve with a lighter hammer, but not hit the max. with heavy bullets with a conventional valve.... at least that has been my experience....
Bob
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I just tried a couple of Airsoft BBs in the 6mm at 2800 psi.... 1944 & 1963 fps.... So much for the 1650 maximum.... *LOL*.... Next time I have the 6mm upper on the unregulated gun I will try a couple of shots at 3800 psi.... maybe even 4200.... ;)
Interestly, Lloyd's spreadsheet predicted 1999 fps for the 1.8 gr. plastic BB.... :o
Bob
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Bob, this project has become quite a learning experience. The velocity you got from those air soft plastic BBs is quite an eye opener!
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I tried to glue up the 0.047" vent through the poppet and redrill it with no success, so today I made a new poppet for my SS Valve.... I am still using the 3/8" big end and 1/4" small end, but I added a thin (1 mm) O-ring inside against the shoulder of the poppet as a bump stop.... It should never touch, but if the valve was driven fully open (or blew fully open) the O-ring bumper would take the shock instead of either the shoulder on the poppet hitting the inside shoulder of the thimble, or the spring going coil-bound.... It was just a safety measure, but also a way to find out if the valve was opening that far.... As I expected, the O-ring made NO difference, which is proof that the valve is not trying to open more than the 0.19" travel before the O-ring hits.... This was a useful piece of information (and expected), and I plan on incorporating this feature into any future SS valves I make to insure they don't break from being overdriven, or from machine-gunning.... I used PEEK for the poppet, not because it was required, but just because I had some and wanted to try it, and it machines nicer than Delrin....
When I reassembled the 6 mm regulated gun I finally nailed it.... I used the 32 gr. MDS hammer, and the 11 lb/in spring with 1 lb. of preload on the SSG guide.... I was able to easily get to the plateau with all three bullets, and have to run 5 turns of SSG gap with the heaviest and 7 turns with the lightest to get about 3% below the plateau, where I want to operate to get reasonable efficiency.... Here is a graph of the velocity vs. SSG gap for all three bullets at 2800 psi....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/6mm%20Plateaus%202800_zpsdgisn6rd.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/6mm%20Plateaus%202800_zpsdgisn6rd.jpg.html)
I am getting nearly 200 fps of adjustment before the valve falls off the cliff, which is plenty, I will never run it that low.... You will note that there is one additional line on the graph, the dotted black line.... I set the SSG gap at 6 turns, and using the 63.8 gr. bullets I tested the velocity adjuster on the back of the receiver that restricts how far the bolt retracts by moving a pin into the J-slot for the handle.... The reason for the slight increase in velocity when the adjuster is turned in 2 turns is that I had to shorten the nose of the bolt 1/16" because it was pushing the bullets too far forward, which made the 73.4 gr too hard to chamber.... This meant that with the bolt handle pulled all the way back in the J-slot it was creating more wasted volume in the chamber, behind the barrel port, which was dropping the velocity slightly.... It shows the importance of minimum wasted volume between the valve seat and the base of the bullet.... From the maximum velocity setting I have 8 turns of adjustment on the 8-32 screw, which moves the bolt nose from the back of the port to nearly obstructing it.... at which setting the velocity is below 500 fps.... The cool thing about this adjuster is that you can easily try different velocities, to find out if there is an optimum for accuracy.... Of course you should adjust the Harmonic Tuner at each velocity, just to make sure what you are seeing is a true velocity effect, not a change of accuracy due to barrel harmonics....
Once I am sure that there are no leaks, I will remove the "tiny tank" and replace it with my 500 cc CF bottle.... At that point I will be able to test the efficiency at various velocity settings.... These two guns are nearing the end of their development, which is a relief because it won't be long before the Motel gets busy and my shop time disappears once more....
Bob
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Bob, All the effort is paying off and you've ended up with a lot of versatility in that set-up. Well done.
Are you pretty much using the SSG on 100% of your projects now?
Thanks,
Lloyd
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I design it into every new project.... Sometimes there was so much hammer strike required (as with my Monocoque) I haven't been able to set it up with a gap and still get full power.... but that should be a thing of the past now with the SS Valve.... Over the next couple of years I will be making more of them to reduce the hammer strike on all of my bullet shooters.... Some of them will be upgraded to larger ports and valve throats whereas they were limited in the past because I couldn't get enough hammer strike.... In reality, I think all my new PCP projects will have bore-area porting, because even with regulated guns and lower power, it seems to be very efficient, and you can run a lower setpoint for a given FPE....
I was just thinking this morning how several relatively new technologies have come together to drastically change PCPs over the last few years.... The SSG gave us the ability to eliminate hammer bounce, and reduce cocking force compared to an SSS with gap.... The drop sear triggers on the MRod and PRod supplied us with readily available, good quality triggers, which allowed the use of MDS hammers.... The MDS hammers made the use of aluminum main tubes more practical.... and of course the SS and Cothran Valves drastically reduced the cocking force, particularly in big-bores.... and allow even lighter MDS hammers without excessive spring force.... The balanced valves also allowed the use of larger valve throats and porting in guns with limited hammer strike capability.... unleashing an FPE capability not previously possible in those configurations....
A decade after I got back into airguns, I suddenly feel like there is so much new to learn.... and that PCPs have entered a new generation.... It's exciting to be a part of it....
Bob
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The gun only lost about 100 psi overnight, so I figure that is "good enough" and I installed the 500 cc CF tank today, and attached the AR style stock.... Here is what it looks like....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/6mm%20Regulated_zpsioo1ovzh.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/6mm%20Regulated_zpsioo1ovzh.jpg.html)
As shown it weighs 8.5 lbs., and without the Harmonic Tuner, exactly 8 lbs.... It balances right in the middle of the tank.... I'm very pleased with the way it came out....
Bob
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...................................
I was just thinking this morning how several relatively new technologies have come together to drastically change PCPs over the last few years.... The SSG gave us the ability to eliminate hammer bounce, and reduce cocking force compared to an SSS with gap.... The drop sear triggers on the MRod and PRod supplied us with readily available, good quality triggers, which allowed the use of MDS hammers.... The MDS hammers made the use of aluminum main tubes more practical.... and of course the SS and Cothran Valves drastically reduced the cocking force, particularly in big-bores.... and allow even lighter MDS hammers without excessive spring force.... The balanced valves also allowed the use of larger valve throats and porting in guns with limited hammer strike capability.... unleashing an FPE capability not previously possible in those configurations....
A decade after I got back into airguns, I suddenly feel like there is so much new to learn.... and that PCPs have entered a new generation.... It's exciting to be a part of it....
Bob
X 2
Bob, I know you realize this, but of the innovations in your list, the drop sear trigger is the only one that came from a company. I'll probably put my foot in my mouth right now, but the bulk of the innovations are from individuals. The larger companies have come up with nicer guns, different air gun designs, more accurate guns, improvements on existing technology, and made the field fairly competitive. But the thinking outside-the-box type of innovations......... hmmmmm.
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I was just thinking this morning how several relatively new technologies have come together to drastically change PCPs over the last few years.... The SSG gave us the ability to eliminate hammer bounce, and reduce cocking force compared to an SSS with gap.... The drop sear triggers on the MRod and PRod supplied us with readily available, good quality triggers, which allowed the use of MDS hammers.... The MDS hammers made the use of aluminum main tubes more practical.... and of course the SS and Cothran Valves drastically reduced the cocking force, particularly in big-bores.... and allow even lighter MDS hammers without excessive spring force.... The balanced valves also allowed the use of larger valve throats and porting in guns with limited hammer strike capability.... unleashing an FPE capability not previously possible in those configurations....
A decade after I got back into airguns, I suddenly feel like there is so much new to learn.... and that PCPs have entered a new generation.... It's exciting to be a part of it....
Bob
X 2
Bob, I know you realize this, but of the innovations in your list, the drop sear trigger is the only one that came from a company. I'll probably put my foot in my mouth right now, but the bulk of the innovations are from individuals. The larger companies have come up with nicer guns, different air gun designs, more accurate guns, improvements on existing technology, and made the field fairly competitive. But the thinking outside-the-box type of innovations......... hmmmmm.
I agree with both of your points of view. Im dreaming up some new ideas right now and as crazy as they seem to me now Im sure in a few months or a year it will be old hat. Its a shame these big companies dont pick up the thinkers and doers in the field but I guess its cheaper to just copy them or just follow trends. Seems more than a few companies could use a Bob or Lloyd if you ask me. But then again maybe the thinkers and doers are happy just the way they are uninhibited by deadlines and bean counters.
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Well the 6 mm regulated gun has been sitting with the 500 cc bottle on it for a few days, and shows no visible drop in pressure after the initial post-fill cooling.... I topped it up from my SCBA tank, with the digital gauge in between, shut off and bled the tank valve, leaving the digital gauge connected to the gun with a microbore hose (there is a check valve on the "inlet" side of the gauge for this purpose).... I took a couple of shots until I noticed the digits dropping on the gauge, so I knew it was accurately reading the pressure in the 500 cc CF bottle, let it stabilize a couple of minutes, recorded the pressure, and shot 10 shots through the Chrony with the 63.8 gr. bullets, with the SSG gap set at 7 turns.... I recorded the average velocity (939 fps), the ES (11 fps) and the SD (2.8 ), and after a couple of minutes for the pressure to stabilize again (it rises slightly after the string as the tank warms back up to room temp) I recorded the pressure again.... The tank dropped 465 psi for the 10 shots (which averaged 124.9 FPE), which means I used 978 std. CI of air to produce 1249 FPE, which works out to 1.28 FPE/CI.... That should give me about 30 shots per fill (with the VanDerWaals correction), and I am very pleased with that.... I can dial the velocity up or down from there, which will lose or gain shots of course.... but I certainly have a good starting point for testing.... It shoots 982 fps with the 58.3 gr. Bowman HPs at this setting.... should be deadly on Varmints....
Bob
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I swapped the 6 mm upper onto the unregulated gun tonight and filled it to its MSWP of 4200 psi.... I set the SSG to just a whisker of gap and fired one shot to settle things, topped it up and fired two shots with the 73.4 gr. bullets.... 1028 & 1029 fps (173 FPE).... Then I did something I have just been dying to try ever since I came up with the idea of building a 6mm.... I loaded up a 1.8 gr. Airsoft BB, topped it up to 4200 psi and took a bead through the Chrony.... 2093 fps.... repeated it.... 2097 fps.... once more.... 2087 fps.... That gives a three shot average of 2092 fps (17.5 FPE) with a basic PCP, just shooting very light ammo.... No special equipment, just a standard SS style valve, porting that turns through 180 deg., and a rifled 29" barrel that is a poor fit on the BB.... it will actually roll out the muzzle if you hold it pointing downwards.... Running air at room temperature (the pressure in the 300 cc reservoir dropped ~ 250 psi each shot), not Helium.... Lloyd still holds the record at 2162 fps.... but he better be looking over his shoulder.... ;D
Bob
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I swapped the 6 mm upper onto the unregulated gun tonight and filled it to its MSWP of 4200 psi.... I set the SSG to just a whisker of gap and fired one shot to settle things, topped it up and fired two shots with the 73.4 gr. bullets.... 1028 & 1029 fps (173 FPE).... Then I did something I have just been dying to try ever since I came up with the idea of building a 6mm.... I loaded up a 1.8 gr. Airsoft BB, topped it up to 4200 psi and took a bead through the Chrony.... 2093 fps.... repeated it.... 2097 fps.... once more.... 2087 fps.... That gives a three shot average of 2092 fps (17.5 FPE) with a basic PCP, just shooting very light ammo.... No special equipment, just a standard SS style valve, porting that turns through 180 deg., and a rifled 29" barrel that is a poor fit on the BB.... it will actually roll out the muzzle if you hold it pointing downwards.... Running air at room temperature (the pressure in the 300 cc reservoir dropped ~ 250 psi each shot), not Helium.... Lloyd still holds the record at 2162 fps.... but he better be looking over his shoulder.... ;D
Bob
Hahahaha....Coming for you lloyd!!!
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I swapped the 6 mm upper onto the unregulated gun tonight and filled it to its MSWP of 4200 psi.... I set the SSG to just a whisker of gap and fired one shot to settle things, topped it up and fired two shots with the 73.4 gr. bullets.... 1028 & 1029 fps (173 FPE).... Then I did something I have just been dying to try ever since I came up with the idea of building a 6mm.... I loaded up a 1.8 gr. Airsoft BB, topped it up to 4200 psi and took a bead through the Chrony.... 2093 fps.... repeated it.... 2097 fps.... once more.... 2087 fps.... That gives a three shot average of 2092 fps (17.5 FPE) with a basic PCP, just shooting very light ammo.... No special equipment, just a standard SS style valve, porting that turns through 180 deg., and a rifled 29" barrel that is a poor fit on the BB.... it will actually roll out the muzzle if you hold it pointing downwards.... Running air at room temperature (the pressure in the 300 cc reservoir dropped ~ 250 psi each shot), not Helium.... Lloyd still holds the record at 2162 fps.... but he better be looking over his shoulder.... ;D
Bob
incredible!! in the airsoft world ,you would be the messiah
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incredible!! in the airsoft world ,you would be the messiah
Most all airsoft fields have FPS limits for a reason.
I saw a guy take a 40 grain plastic BB at 550 fps from 5 feet in the back of the head and it embedded nearly to his skull. Took our EMT 15 minutes to get that bb out, with lots of pain. The guy almost passed out. I think a BB that fast could actually kill someone from close enough. Snipers in airsoft generally aren't supposed to shoot from less than 100 ft at most fields, but this guy ran right in front of a teammate when he was breaking a shot.
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incredible!! in the airsoft world ,you would be the messiah
Most all airsoft fields have FPS limits for a reason.
I saw a guy take a 40 grain plastic BB at 550 fps from 5 feet in the back of the head and it embedded nearly to his skull. Took our EMT 15 minutes to get that bb out, with lots of pain. The guy almost passed out. I think a BB that fast could actually kill someone from close enough. Snipers in airsoft generally aren't supposed to shoot from less than 100 ft at most fields, but this guy ran right in front of a teammate when he was breaking a shot.
War is *(&^ LOL.
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There is no way that a 6 mm plastic BB could ever weigh 40 gr.... In fact a lead roundball that is 6 mm would only weigh 20 gr.... There is no question that a 2000+ fps shot with this 1.8 gr. plastic Airsoft BB could kill you at close range.... The BC, however, will be VERY low, on the order of about 0.003, so it will lose velocity and energy very quickly.... It should fall subsonic in about 8 yards, and at 40 yards be down to under 400 fps.... In fact with my Chrony at about 1 yard, the MV would likely be around 2300 fps....
Bob
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Sorry Bob, I meant .40 grain as opposed to the normal .20 grain that are usually used.
https://www.evike.com/products/63208/ (https://www.evike.com/products/63208/)
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Ahhhhh.... you are talking GRAMS (g.), not GRAINS (gr.).... a 0.20 g. BB would weigh 0.20 x 15.43 = 3.1 grains.... and a 0.40 g. BB would weigh 6.2 grains.... The ones I have are only 1.8 gr. = (0.12 g).... By the looks of it those are the lightest available.... which for achieving high velocity is just the ticket....
Bob
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Nice one Bob, gun looks very good!
Not to take anything away from you but Lloyd was shooting lead pellet not plastic if I remember correctly.
;)
Marko
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Nice one Bob, gun looks very good!
Not to take anything away from you but Lloyd was shooting lead pellet not plastic if I remember correctly.
;)
Marko
LLoyds sectional density was about the same , it was super light 9mm.as I recall.. it was still higher though , havent done the math
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Bob
Could you use a #4 buckshot pellet, approx .240" dia and right around 20.5 grs in weight,
it might provide a better seal and possibly better fps, for the psi used etc.
You said, the 6 mm air soft pellet would roll out the bbl, so you are getting lots of blow by.
Tia,
Don
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Don, at 20 gr. the velocity would be wayyyyyyy lower.... something around 1500 fps.... I don't actually think the blow by is that important in this case.... The plastic BB is soooooo light it is just getting carried along by the huge cloud of air exiting the barrel.... which is about the same weight as the 73.4 gr. lead bullet with this length of barrel and pressure.... It's the air that is coming out at over 2000 fps, and the 1.8 gr. BB is just going along for the ride....
Bob
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Although I plan on running the .257 barrel on the unregulated gun, while I had the upper removed to try the 6 mm on it, I thought I would try the .257 upper on the regulated lower.... It had a slight leak in the transfer port area, but I did my testing anyways.... Here are the results for the 73.5 gr. Lyman 257420 at 2800 psi....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/257%20Plateaus%202800_zpsd0uejkoy.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/257%20Plateaus%202800_zpsd0uejkoy.jpg.html)
At 5% below the maximum velocity I was at 894 fps (130 FPE) at 8 turns of gap on the SSG, and the efficiency was 1.17 FPE/CI.... While that is similar to what I was getting on my .257 Hayabusa, it was a little below the 1.28 FPE/CI I got on the previous testing, which I attribute to the leak.... I was either losing a bit of velocity (likely), using more air (unlikely), or both.... but no question it would affect the FPE/CI either way.... If I was going to set this gun up as a regulated .257 I would likely bump up the setpoint pressure to 2900-3000 psi, although that may not be necessary with the 66 gr. HP version I have of this bullet, it might well shoot better at this pressure....
This pretty much completes the basic testing of these two guns.... I am extremely pleased with the results for both power and efficiency.... The plan is to put the 6 mm upper back on the 2800 psi regulated gun and run the .257 barrel on the unregulated version, and tethered it at 3800, but tune it for a few shots off tether.... All I hope now is that the snow disappears before the Motel gets too busy so that I have a chance to see how they shoot....
Bob
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Bob,
That 1.8 gr plastic BB is indeed just going along for the ride with the air exiting the muzzle, and yes, I am looking over my shoulder, LOL. ???
I owe a few people a return to the max velocity project with high pressure nitrogen. You have probably reached the point with the plastic BB where the rate-of-opening of the valve is the major limiting factor. With the max vel guns, the projectile was to be held in the breech like a cork with full pressure behind it, and then the cork was allowed to pop out instantly by a mechanism akin to a drop-away sear. You haven't, by any chance, made a nice snug fitting plastic pellet for that new 6mm, have you, you rascal? ;)
Lloyd
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Nope, the BB is so loose that if you hold the muzzle down it rolls out onto the floor.... MV about 1 fps.... Kind of the opposite of holding it in the breech for the pressure to build, just let it "go with the flow", so to speak....
Perhaps that idea I was talking to you about regarding the pressure at the pellet taking only about 0.05 mSec. to build (and virtually no "mass airflow" during that time) is showing up here.... The pressure is at full value before the BB has moved more than an inch at most, so I still have 28" available for acceleration?.... The BB is so light, the air being accelerated weighs about 40 times as much.... ::)
Bob
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Hey Bob, I went through the project again, but didn't find dimensions on your AliExpress carbon fiber tank. Perhaps I skimmed right over it, if so I apologize. I'd appreciate it if you could tell us the dimensions, diameter, length, weight and thread size. The reason I'm asking is that I just broke down my Hatsan Nova and was thinking it'd be nice to have a carbon fiber tank instead of the 31.2 oz aluminum tank that comes from the factory. Then I recalled you using the chinese tank on this build. Then I found out that Altaros builds a regulator for the Nova. Now the wheels are REALLY spinning. But I digress. (weird how that happens). Thanks in advance if you can supply the info on the tank. I'm thinking you ordered one like this?
https://tinyurl.com/AliExpressCarbonFiberTank
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Yes, Paul, that is the tank I bought.... 500 cc, 4500 psi, 18 mm x 1.5 mm threads, 60 mm diameter (actually a bit over where the label is, call it 2.4"), 21 oz. in weight, and the length is 11.5" without regulator....
Bob
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I swapped the 6 mm upper onto the unregulated gun tonight and filled it to its MSWP of 4200 psi.... I set the SSG to just a whisker of gap and fired one shot to settle things, topped it up and fired two shots with the 73.4 gr. bullets.... 1028 & 1029 fps (173 FPE).... Then I did something I have just been dying to try ever since I came up with the idea of building a 6mm.... I loaded up a 1.8 gr. Airsoft BB, topped it up to 4200 psi and took a bead through the Chrony.... 2093 fps.... repeated it.... 2097 fps.... once more.... 2087 fps.... That gives a three shot average of 2092 fps (17.5 FPE) with a basic PCP, just shooting very light ammo.... No special equipment, just a standard SS style valve, porting that turns through 180 deg., and a rifled 29" barrel that is a poor fit on the BB.... it will actually roll out the muzzle if you hold it pointing downwards.... Running air at room temperature (the pressure in the 300 cc reservoir dropped ~ 250 psi each shot), not Helium.... Lloyd still holds the record at 2162 fps.... but he better be looking over his shoulder.... ;D
Bob
Bob,
I am looking at this again and the wheels are turning and questions are coming out, LOL.
Full bore porting?
How much clearance on the bb? Maybe a thou or 2?
250 psi drop for the shot. Do you think the valve was open for the full barrel length?
Really loud? Did you have the chrony clamped down, ha, ha?
What secrets are you holding back, LOL?
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Yes, full bore-area porting, with retractable bolt.... The diameter of the BB is about 0.002" less than the lands, and about 0.010" less than the grooves.... The valve was definitely open until long after the BB left the muzzle.... The best model I had using your J4 spreadsheet for the 73.4 gr. bullet which I also tested at 4200 psi was a dwell of 0.0036 sec @ 67%.... just shy of a dump shot.... 1029 fps with ~250 psi drop in pressure = 0.55 FPE/CI.... Since I was using my SS valve, when I used the 1.8 gr. BB the valve may not have had the same dwell, even though it did have the same hammer strike.... the dwell may have been a bit less, or more?....
I can't swear if the pressure drop was still 250 psi when I used the 1.8 gr. BB, and I was only using the small 1" gauge on the gun anyways.... maybe it was closer to 300 psi?.... I admit to being more interested in the velocity and how consistent the 3 shots were.... No, the Chrony wasn't clamped down, but I didn't blow the diffusers and lights off it.... the key is that it was so consistent I have no reason to doubt the results....
No secrets, WYSIWYG.... ;D
Bob
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Bob,
Given the fact that you were using a 29" barrel and I was using a 46" barrel, if we extrapolate the velocity in your gun to 48", the velocity is about 2305fps, quite a bit faster than my 2162fps. But it also seems that the difference in projectile weight, 1.8gn vs 7.7gn could account for that difference in velocity. In other words, well done Bob.
It appears that your 1.8gn BB might actually be leading the front edge of the expanding air in the barrel, almost like surfing.
All of these velocities are well above Mach 1, so what about choked flow? How is it limiting the velocity... or is it limiting the velocity?
After some serious reading, I believe that, just as the 1650fps velocity limit was the result of the misapplication of a physics principle, we have been misapplying the idea of choked flow inside an airgun. Please correct me if I am wrong, BUT: We have been saying that if the velocity through the most restricted passage within the flow path exceeded Mach 1, the flow would become choked. Actually, that is false. What really causes choked flow is the pressure drop across the restricted section, and a pressure drop of almost 50% is required to cause choked flow. I believe that the only time there will be a pressure drop that great is the instant (a few micro seconds) the valve poppet lifts off the seat, and the final instant as the poppet closes.
Here is my reasoning. Before the shot, the bullet is wedged into the breech end of the barrel just like a cork. The bullet has mass that must be accelerated out of the barrel. As soon as the valve opens, the air blasts past the valve poppet and starts to stack up behind the bullet. As soon as the air starts to stack up, the pressure differential within the system becomes very low (less than 10%, maybe?), and certainly nowhere near the 50% needed to cause choked flow. As the bullet starts to move, it is still acting like a cork for the expanding air, and the pressure differential is still very low because the air is building up faster than the bullet is accelerating. That magical 50% pressure drop never occurs within the system, and therefore choked flow does not occur, even though the velocity of the bullet and a major portion of the air column greatly exceed Mach 1.
Consider this as additional proof. Given a gun operating at 3000psi with .25 cal and .25" passages, a 20% pressure drop across the valve could produce a flow rate of 2000scfm, which is 57,600 standard cuin/sec, or 57cuin/millisec. Considering the fact that most of our guns will produce about 1 fpe/cuin, and the valve open time might vary in the 1.5 to 5 millisecond range, that 20% pressure drop across the valve is probably quite adequate for a .25 cal system. Now, if the pressure drop goes to 40% (as with a very light projectile) the flow rate increases to about 74 cuin/millisec. So even though the pressure drop doubled, the mass flow did not. But the real point is that we are almost always, IMO, operating safely below the that 50% pressure drop that would initiate choked flow. Therefore, no choked flow!
Is this what is really happening? It certainly makes a lot of sense and explains what our empirical data demonstrates.
Lloyd
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WOW, JUST WOW !!!
just as the 1650fps velocity limit was the result of the misapplication of a physics principle, we have been misapplying the idea of choked flow inside an airgun.
Lloyd, I think you may have a SOLID REASON for the lack of choked flow.... insufficient pressure differential.... This may be a chicken-and-egg problem and we have been looking at it from the wrong end of the chicken !!!
We have been saying that if the velocity through the most restricted passage within the flow path exceeded Mach 1, the flow would become choked. Actually, that is false. What really causes choked flow is the pressure drop across the restricted section, and a pressure drop of almost 50% is required to cause choked flow.
We have been saying "well the flow is supersonic, so it must be choked, which causes a 50% pressure loss".... when in fact we SHOULD have been saying "nowhere in the system (with one exception below) is the pressure differential approaching 50%, so even though the flow is supersonic, it is NOT choked".... BRILLIANT, MY FRIEND.... SIMPLY BRILLIANT....
The exception I mentioned above is when the poppet is CLOSING only, just before the poppet touches the seat.... At that point the flow rate is high (as is the velocity of the pellet and air column), but the area under the poppet is decreasing, and the pressure differential increasing.... When it reaches 50%, the flow chokes for a few microseconds before the valve shuts.... At the other end of the shot cycle, when the valve is opening, there is no comparable choking because all the air is doing is filling the dead space between valve seat and pellet (which is stationary), so there is no real flow volume or air velocity, beyond the random vibration of the air molecules, so no choking....
I was playing with your two spreadsheets last night (the unchoked and choked versions), and they both underpredict the velocity of my shot, with the choked version predicting a lower value.... I think you are correct that in the case of this ultralight BB, it is "surfing" the front of the moving wave of air, which is expanding away from the valve instead of being contained inside the barrel by the mass, inertia, and friction of the projectile.... There is no question in my mind that the difference between my 1.8 gr. BB and your 7.7 gr. "pellet" is the big reason for the ease with which I broke 2000 fps.... Let's face it, it doesn't get any easier than what I did.... ::)
Bob
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I think I have to revisit the math behind my internal ballistics spreadsheet now, LOL. The choked flow part in the spreadsheet is definitely wrong, but I think the VanDerWaals pressure/density enhancements need to be incorporated. I was noticing, like you did, that the eff in the spreadsheet had to be above 1 for the numbers to work.
The lively discussion that you and subscriberand MJP were having on Travis's wing-ring thread really pushed me into trying to make sense of this air flow. Stuff just seemed intuitively wrong, and that always bothers the heck out of me. So even though I was mostly just lurking on that thread, POW, it turned the light bulb on!
This forum is great!
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This is very interesting!!! So how do we test this theory? Do we put the parameters to be tested into a spreadsheet and adjust the constriction of the TP or air column and measure speed and air used or ??? Not sure how to go about proving or dis proving.
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This is very interesting!!! So how do we test this theory? Do we put the parameters to be tested into a spreadsheet and adjust the constriction of the TP or air column and measure speed and air used or ??? Not sure how to go about proving or dis proving.
I think it is all in the math, and that we just weren't applying the physical laws correctly. I don't think physical testing is required to prove or disprove.
Take a look at this lively discussion, which is where my research started.
https://www.physicsforums.com/threads/velocity-of-air-coming-out-of-a-nozzle.694656/ (https://www.physicsforums.com/threads/velocity-of-air-coming-out-of-a-nozzle.694656/)
If you branch out from this Physics Forum thread, all the information supports what I stated.
Lloyd
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Travis, we pretty much already have the proof.... Lloyd and I have been trying to incorporate choked flow into his spreadsheet for a few years, and every attempt has failed and we didn't know why.... NOW we have the answer.... It is very much a case of the facts didn't fit the theory, so it was time for a new theory, or at least a fresh LOOK at what we thought the theory was saying.... exactly like the "1650 fps limit" which Lloyd blew out of the water, and we spend the better part of a year trying to figure out why.... The two effects are somewhat related, with the "cork in the bottle" effect of the pellet keeping the pressure high in the barrel during the time the valve is open (avoiding choking), while the volume under pressure increases as it is "topped up" from the reservoir at the breech end (pushing the air already in the barrel along in "packets", with the molecules in each packet vibrating at 1650 fps) and so allowing the muzzle velocity to exceed that proposed 1650 fps limit....
This, for me, was a true "lightbulb moment".... and thanks to Lloyd I now have a much better and more complete understanding of what happens inside a PCP.... and why we can do things some said were impossible.... I agree with Lloyd that we need to drop the idea of choked flow from the spreadsheet, but we do need to incorporate the VanDerWaals effect on the mass of air used per shot, instead of just using the Boyle's pressure/volume relationship.... which breaks down over 2500-3000 psi.... It won't make any significant difference to 90% of our calculations.... but it will show up for those few high-power, high-pressure applications.... At least we won't need to use the Speed of Sound calculations in your spreadsheet any longer.... ::)
BTW, Lloyd, I saw a tank fill calculator the other day which has the VDW correction in it.... it uses the air MASS leaving the source tank to top up the air MASS in the receiving tank/reservoir.... It doesn't tell you it does that, but the results indicate that to be the case....
Bob
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Travis, we pretty much already have the proof.... Lloyd and I have been trying to incorporate choked flow into his spreadsheet for a few years, and every attempt has failed and we didn't know why.... NOW we have the answer.... It is very much a case of the facts didn't fit the theory, so it was time for a new theory, or at least a fresh LOOK at what we thought the theory was saying.... exactly like the "1650 fps limit" which Lloyd blew out of the water, and we spend the better part of a year trying to figure out why.... The two effects are somewhat related, with the "cork in the bottle" effect of the pellet keeping the pressure high in the barrel during the time the valve is open (avoiding choking), while the volume under pressure increases as it is "topped up" from the reservoir at the breech end (pushing the air already in the barrel along in "packets", with the molecules in each packet vibrating at 1650 fps) and so allowing the muzzle velocity to exceed that proposed 1650 fps limit....
This, for me, was a true "lightbulb moment".... and thanks to Lloyd I now have a much better and more complete understanding of what happens inside a PCP.... and why we can do things some said were impossible.... I agree with Lloyd that we need to drop the idea of choked flow from the spreadsheet, but we do need to incorporate the VanDerWaals effect on the mass of air used per shot, instead of just using the Boyle's pressure/volume relationship.... which breaks down over 2500-3000 psi.... It won't make any significant difference to 90% of our calculations.... but it will show up for those few high-power, high-pressure applications.... At least we won't need to use the Speed of Sound calculations in your spreadsheet any longer.... ::)
BTW, Lloyd, I saw a tank fill calculator the other day which has the VDW correction in it.... it uses the air MASS leaving the source tank to top up the air MASS in the receiving tank/reservoir.... It doesn't tell you it does that, but the results indicate that to be the case....
Bob
Bob I think you guys are right now I have to go retest some flow dynamics in my CFD program Ill be right back.
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Heres a link to the opensource CFD I play with If you want to Geek out with me LOL.
https://www.openfoam.com/download/install-binary-windows.php (https://www.openfoam.com/download/install-binary-windows.php)
this will help also https://www.youtube.com/watch?v=AJESwh-QfSo (https://www.youtube.com/watch?v=AJESwh-QfSo)
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I don't know of any CFD program that allows you to "put a cork in the barrel" and keep adding air from one end while partially restricting it at the other.... but then I haven't played with them much either....
Bob
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Yes, Paul, that is the tank I bought.... 500 cc, 4500 psi, 18 mm x 1.5 mm threads, 60 mm diameter (actually a bit over where the label is, call it 2.4"), 21 oz. in weight, and the length is 11.5" without regulator....
Bob
Thanks, Bob! I've still not managed to pull the valve or whatever it is in the end of the tank so am not sure on the threads. The rest? Looks VERY interesting! The factory bottle is about 12 inches long, it's just a hair over 60 mm diameter and weighs 31.2 oz. The rifle is rated at 250 bar. So now I'm REALLY cogitating. ;D Shaving 10 oz off the rifle would be welcome indeed. OK. I'll quit hijacking your thread. The info is GREATLY appreciated!!!
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I don't know of any CFD program that allows you to "put a cork in the barrel" and keep adding air from one end while partially restricting it at the other.... but then I haven't played with them much either....
Bob
Thats exactly what I went to the garage to try with OpenFoam. I sent in a Email to the developers to help me out I couldnt figure it out on my own :-[ But I dont give up that easy so as soon as I get some help I will give it a go ;D
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The choked flow discussion that I was pushing seems to be hijacking Bob's thread a bit too much, so I have started its own, totally fun, totally geek, topic. If you just shake your head an look away from the new topic, I understand, it's kinda sick. ;)
Choked flow discussion new location
https://www.gatewaytoairguns.org/GTA/index.php?topic=142095.new#new (https://www.gatewaytoairguns.org/GTA/index.php?topic=142095.new#new)
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I wanted to add a note to this thread, to give you an idea of what I have in mind for future development of these two PCPs.... If you have followed along, I have two complete lower assemblies, one regulated with a 150 cc plenum at about 3000 psi, with air supplied from a 500 cc, 300 bar bottle.... and the other unregulated with a 300 cc reservoir with a 4200 psi MSWP.... It would normally be tuned to be tethered at about 3800 psi, with a few shots off bottle....
I have two interchangeable uppers for these guns, with single shot actions which accept a 14mm OD barrel with a 20mm carbon sleeve, one in 6mm (0.243) and the other in .257 cal. and both 28" long with a 10" twist.... I am in contact with Mike at TJ's about the possibility of getting two more 28" barrels that I can fit to these uppers.... One will be his 0.172" barrel in the 9" twist, to shoot the 26 gr. NOE bullet, like Cedric is using.... The other will be a .224 cal in a fast twist, either 8 or 10", to shoot the longer FB bullets and hopefully my BBTs, in the 55-75 gr. range.... It is likely the .17 cal will go on the regulated lower, and the .22 cal on the unregulated, but since the receivers are interchangeable, they could fit either....
I don't know when this project will see some action.... but I just wanted you to know I am exploring the possibility of using smaller calibers on these two PCPs.... Whether this proceeds at all depends on what Mike can supply that can be fitted into my existing receivers.... as I really don't want to make two new receivers for the new calibers.... Any serious testing of the existing 6mm and .257.... and of course anything new.... will still have to wait until we close the Motel in 2021.... but it would be nice to have them ready for testing that summer.... 8)
Bob
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Bob, I am really happy that you also planning to taste lower calibers. Which is your grouping with .243 and .257 slugs at 100 yd with 10” twist ?
Do you have some ( 1-10 %) flyers or no any ?
You probable have notice that I am awaiting for FX STX .177 slug liner "P" usable for 21gr. Piledriver.
I believe them a lot.
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Peter, I haven't had a chance to even shoot either gun outside.... The Motel prevents me from having time to shoot in the summer, and we have snow on the ground all winter.... Testing will likely have to wait until 2021 when we close the Motel....
Bob