GTA
Airguns by Make and Model => Crosman Airguns => Topic started by: Spooner on July 03, 2021, 03:53:34 PM
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with my first 1377 that i re-modded, i was never able to determine why i couldnt get the pump arm to adjust to the 30 degree range at ten pumps? doesnt make any sense but something is not right. my newest one with along with my re-modded 1322 are the two i use all the time anyway, so i am going to tear down the first 1377. maybe i got some shavings in the flat top valve when i pinned it, not sure, but gonna open that up and check just to be sure. there really isnt anything else that could be causing this but maybe something will stand out when i take it apart?
having said that... i am going to build it back as a .22, but this one will be with an 18" Crosman barrel. i am not a big fan of Crosman barrels but since MAC1 does an accuracy prep and includes the extended bolt probe... it is at a price point that is very affordable, so i went with that. its really just a project gun to have some fun with and i have never used an 18" barrel before... should be interesting. ;) 8)
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well... not sure but i think i found the problem? it looks like when i drilled into the valve i may have gone just a tiny bit too far. it didnt go through the valve but i can see a spot inside where the poppet seals against the inner flange where there is a small raised bump that is right in line with where i drilled. i am guessing that when the poppet closes off the valve that it is allowing air to go back against the piston causing the pump arm to spring back out farther than the 30 degrees. it doesnt leak air and it doesnt spring all the way open, so i am just not sure? it would make sense though.
this presents a problem for pinning the new valve (which i just ordered from Mellon) because i am going to have to drill the new valve to align perfectly with the threaded hole that i drilled/tapped in the pump tube without screwing up the tapped threads in the tube. my only idea is to put in the new valve, align it, draw around the hole with a pencil, drill it outside the tube and pray it is aligned when i put it back in. i guess if i am really careful, i can do it with the valve in place inside the tube, but i would have to be very careful not to hit the threads in the tube.
has anyone ever had to replace a valve under these circumstances? suggestions greatly appreciated.
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Hi Robert,
I'll try to answer your second question first... Sure, I've done it lots of times. I install the valve (secured of course) and drill the valve thru the existing drill hole in the tube. No big deal. You may truncate some of the female threads in the tube but that's not an issue... it shouldn't open up any more than if you had used the recommended tap drill (#29)... which is .136" vs. the .125" 1/8" bit.
I can't picture the raised bump issue. You shouldn't be able to see where you drilled the valve (from the inside), even if you broke thru, because it should be entirely within the small diameter inlet. My guess is that you have a headspace issue... Is it really a problem?... i.e. poor performance issues?
Another way to check if you have headspace issues (at the higher pressures) is with the number of pumps it takes before your piston no longer makes contact with the valve at the end of the stroke... You should be able to feel the contact... btw, that's when I stop the pump stroke... no need to fully close the forearm when both flattop faces are already pressed together. Anyway, for mine, they make noticeable contact for the first 5 or 6 pumps... hth-
Wyo
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Hi Robert,
I'll try to answer your second question first... Sure, I've done it lots of times. I install the valve (secured of course) and drill the valve thru the existing drill hole in the tube. No big deal. You may truncate some of the female threads in the tube but that's not an issue... it shouldn't open up any more than if you had used the recommended tap drill (#29)... which is .136" vs. the .125" 1/8" bit.
I can't picture the raised bump issue. You shouldn't be able to see where you drilled the valve (from the inside), even if you broke thru, because it should be entirely within the small diameter inlet. My guess is that you have a headspace issue... Is it really a problem?... i.e. poor performance issues?
Another way to check if you have headspace issues (at the higher pressures) is with the number of pumps it takes before your piston no longer makes contact with the valve at the end of the stroke... You should be able to feel the contact... btw, that's when I stop the pump stroke... no need to fully close the forearm when both flattop faces are already pressed together. Anyway, for mine, they make noticeable contact for the first 5 or 6 pumps... hth-
Wyo
drilling the valve installed shouldnt be an issue. i checked the 1/8" drill bit in the threaded tube hole and there is clearance enough to do it without damaging the threads just like you said. i just have to make sure it is correctly positioned on the drill press. i will be ok with that part of this.
with the bump inside the valve. when i did the pinning on this one, i measured around the pump tube to the opposite side of the trigger frame screw then i set the hole back from that position by one hole size to get it away from the o-ring on the end of the valve. the other two i did, that hole was right against the o-ring. what i didnt realize, was that by doing this, i moved the hole from the thicker inlet part of the valve back to the larger open area of the valve where the wall thickness is thinner. at 1/4" deep from the top of the pump tube, it didnt blow through, but it did push the aluminum at the bottom of the hole and formed a bump on the inside of the valve right at the seat where the poppet/ check valve seals against the flange that keeps the air inside after each pump. i messed up by doing this :(. i didnt realize there was such a fine line from thick to thin in the valve wall thickness.
i can still pin it there, but i am going to have to do a shorter hole depth in the valve and grind down the set screw a little shorter. i may just get another pump tube and start over? i have to take some measurements with my calipers, figure out what i have to work with, then decide... but i am leaning towards a new pump tube at this point and just starting over with the hole in the correct place?
with performance, yes, it had (as a 1377) significantly lower FPS then my other 1377... by 60 FPS. same exact configuration and mods. i worked on the piston setting several times but couldnt get it to adjust right. the other 1377 and the 1322 when adjusted with the piston o-ring off went perfectly. 1/2" from close with the o-ring off and roughly 30 degrees at 10 pumps with the o-ring on. this one, if i adjusted it to make contact with the piston at 1/2" from close with the o-ring off then pumped it to 10 times with it on and assembled... it was in the neighborhood of about 80 degrees at 10 pumps? definitely too much head space when there shouldnt be? i checked for all the usual stuff... bent linkage, slop, pump arm damage, ect, but it is all no different then the other two modded guns. it is very strange.
Thanks Wyo... I appreciate your help with this! ;D
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this morning i opened up the first valve that i actually drilled through when doing the re-mod on this gun, and compared to this second valve with the bump inside. sure enough... my decision to set the pin hole farther back by one hole diameter was a big mistake... i screwed up doing this :(. if it hadnt been for the fact that the bump is inside the valve and at the seat for the check valve, i could have simply re-pinned it from the side and been done. wouldnt have been as clean or pretty but would have worked. bottom line is... there is damage to the valve that i cant work around.
decision made... new pump tube ordered and will start from scratch. i will have to deal with the head space issue when i get to that point as it will take several weeks to get the new valve from Mellon.
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got my new pump tube and got it deburred. also drilled the hole for the new valve which shipped from Mellon this morning. the metal barrel band from Maverick Custom Airguns came yesterday as well... this is a REALLY nice barrel band! this barrel band is a little pricey but well worth it. its design and craftsmanship are exceptional! it should hold the 18" barrel very well.
just waiting on the 18" prepped barrel from Mac1 to ship and the valve from Mellon to arrive. 8)
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my accuracy prepped Crosman 18" barrel came from MAC1. they do really nice work! they re-crowned the end, polished the pellet feed end, very nice custom brass extended bolt probe (no handle though) and a hammer spring guide. all said and done... $63. really good price! 8)
I ordered a SS bolt probe from Mellon with the valve and that is the one i will probably use as it comes with the handle and i really like the design of it overall. tracking label is posted but not yet shipped. i am looking forward to seeing what an 18" barrel will do? ;D
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all the bits a pieces have come in and i have it re-assembled. i dont have the LDC or the shoulder stock on yet but am ready to do some chrony checks. probably a day or so for that.
question to the experts...
when i had this gun as a modded 1377, i had the piston adjusted at 1/2" from close and you may remember from that thread that at 10 pumps it was opening to about 70 degrees or so when it should be around 30 degrees. no matter what i have done... it is still the same. this has a .22 / 18" barrel, new Mellon FT valve/piston (pinned), and a new pump tube. it is adjusted exactly to 1/2" from close but still opens to about 70 degrees at ten pumps? i have checked it for excess oil, mis-alignments, weak points in the pump arm assembly, removed every bit of slop i could. it is clean, free of any mistakes, and very smooth in its action. for some reason... this one gun no matter what i do seems to just have to be this way and i dont have a clue why it is so different from the other two i modded? it definitely acts like excessive head space, but i do not know how that can be since i have the 1/2" from close (adjusted without the o-ring on) with the piston adjustment???
the only changes i made were cosmetic. i added the old style barrel spacer, and Mellon .22 extended bolt, and the MCA aluminum barrel band. none of these things would affect this, so i dont know? i will do some chronies tomorrow or the next day. if i can get close to or above 500FPS at 10 pumps... i am going to call it a day. i dont know what else to do with this one?
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Hi Robert,
I can’t (maybe someone else can) diagnose what, if anything, is wrong with your new project gun. But you wouldn’t be the first to have different performance levels from similar or identical builds.
The chrony testing should let you know if there is a problem and to what extent. Until that’s done, who knows.
But in the mean time there are some additional things that can improve pump stroke efficiency…
(https://i.imgur.com/IB1mkiC.jpg)
1. The valve return spring is lighter than stock and allows more of the pump stroke into the valve (less differential pressure is required to crack open the check valve).
The one shown is McMaster Carr # 1986K83
2. The stainless dowel occupies most of the headspace volume in the inlet and again, more of the pump stroke will go into the valve. McMaster # 98380A419
3. Cutting the flanges to about .020” puts the o-rings closer on the TDC compression stroke so again, less headspace and more of the pump volume goes into the valve.
4. Using 90D o-rings will have less extrusion and less headspace volume in the o-ring glands. Certainly this can be done for the valve o-ring but may give you an
unacceptable sliding seal on the piston… I’ve gone both ways 70D and 90D on the piston.
5. Adding more valve volume is a great idea for a long barreled 22 cal. Esp. at higher pumps. Consider that there is a maximum pressure that your pump can obtain
regardless of how many times you pump. With more valve volume you get more of each pump stroke into the valve… i.e pump efficiency doesn’t drop off as fast
because pressure rises slower.
There’s a lot more to it than that (the condensed version above), but no one wants to read 50 pages in one post… or type it for that matter :o … hth-
Wyo
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Thanks as always Wyo. 8)
most of this i am not set up machining wise to do with any precision. things like to cast urethane o-rings i may have in my 1077 seals, and the valve spring from mcmaster-carr i have if those are the same springs you discussed in pm along with the mrod poppet which i also have. i took one of the damaged flat top valves and tried to angle the TP port. i can do that much "so-so" with a dremel and small ball bit but it wasnt great. i would have to farm the machining stuff out to someone with the proper equipment.
the pumping is actually very easy, very smooth. just to eliminate it, i put in my spare new pump arm assembly hoping it was something with that since it is the only thing that remained the same between both builds, but it does the same thing. its a mystery and i have nothing left to try. i get some chronies ran in the next day or two and see where it stands. if it can get to 500fps at 10 pumps, im good. if not, i give it a rest and decide what to do later. i have a modded 1377 and 1322 that both perform flawlessly so i dont have to be in a hurry to decide just how far i want to go with it. i cant spend any more money on this one. i have spent too much already. ;)
what ever the issue is with this one, it doesnt seem to want to be found? Chronies will be the deciding factor. ;)
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did one shot with the chrony at each level, 5.5" TKO LDC attached, Crosman tuned 18" barrel.
5 pumps - 399 / 5.1
10 pumps - 503 / 8.0
15 pumps - 550 / 9.6
20 pumps - 574 / 10.5
no residual air at 20 pumps. pumping is smooth and easy all the way up. these are decent, and i got it to just above my 500 FPS goal at 10. not as high as i have seen in similar setups, but decent for what it is with the issue it has.
@Wyo... believe it or not i actually understand what the picture you posted above represents. shocking, but yeah... i understand. with Mellon FTP's you have a derlin piston. machining that down, it would be my fear that the seal flange would be to thin and flimsy to hold. there are a few things i can do from that pic... the spring, cutting down the valve threads, shaping, and the dowel pin which i will look up on MMC. how did you get that pin to stick in the poppet? im not ready to scope this gun and wrap it up just yet. i will take a few days to consider what i may have missed, just to be thorough, then decide whether to wrap it up or move towards the things i can do in that pic.
i am always grateful when you chime in... you give me new things to learn and consider... thanks! ;D
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did one shot with the chrony at each level, 5.5" TKO LDC attached, Crosman tuned 18" barrel.
5 pumps - 399 / 5.1
10 pumps - 503 / 8.0
15 pumps - 550 / 9.6
20 pumps - 574 / 10.5
no residual air at 20 pumps. pumping is smooth and easy all the way up. these are decent, and i got it to just above my 500 FPS goal at 10. not as high as i have seen in similar setups, but decent for what it is with the issue it has.
@Wyo... believe it or not i actually understand what the picture you posted above represents. shocking, but yeah... i understand. with Mellon FTP's you have a derlin piston. machining that down, it would be my fear that the seal flange would be to thin and flimsy to hold. there are a few things i can do from that pic... the spring, cutting down the valve threads, shaping, and the dowel pin which i will look up on MMC. how did you get that pin to stick in the poppet? im not ready to scope this gun and wrap it up just yet. i will take a few days to consider what i may have missed, just to be thorough, then decide whether to wrap it up or move towards the things i can do in that pic.
i am always grateful when you chime in... you give me new things to learn and consider... thanks! ;D
Hi Spooner. A friend of mine has a 13xx gun with a 18'' .22 barrel, steel breech, and it has a Crosman 66 pump tube and link and FTP/V. It shoots @ 525 fps on ten pumps with CPUM 14.3 grains. Being your gun has the stock, shorter 13xx tube, FWIW I think your current velocity numbers are pretty good. Cheers!
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A 1322 with a FT, steel breech and 18" barrel can easily make 550 FPS with 10 pumps.
Not into golf, but that's par for the course, 600+ FPS is very doable depending on valve volume etc.
So what's holding your gun back?
If you want to be a high velocity player and make big power you need to call in the......Heavy Metal.
Adjustable full metal FT piston and barrel band, counterbore the valve and barrel, .154" TP.
My 1322 Medalist makes 565 FPS with an 18" barrel, steel breech, lightly modified valve, and adjustable cone piston.
It'll do over 600 FPS with a highly modified valve.
https://www.gatewaytoairguns.org/GTA/index.php?topic=185619.msg156145390#msg156145390 (https://www.gatewaytoairguns.org/GTA/index.php?topic=185619.msg156145390#msg156145390)
This 13xx used all the tricks I could throw at it minus the kitchen sink....LOL.
https://www.gatewaytoairguns.org/GTA/index.php?topic=164421.msg155834890#msg155834890 (https://www.gatewaytoairguns.org/GTA/index.php?topic=164421.msg155834890#msg155834890)
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Hi Robert,
I can’t (maybe someone else can) diagnose what, if anything, is wrong with your new project gun. But you wouldn’t be the first to have different performance levels from similar or identical builds.
The chrony testing should let you know if there is a problem and to what extent. Until that’s done, who knows.
But in the mean time there are some additional things that can improve pump stroke efficiency…
(https://i.imgur.com/IB1mkiC.jpg)
1. The valve return spring is lighter than stock and allows more of the pump stroke into the valve (less differential pressure is required to crack open the check valve).
The one shown is McMaster Carr # 1986K83
2. The stainless dowel occupies most of the headspace volume in the inlet and again, more of the pump stroke will go into the valve. McMaster # 98380A419
3. Cutting the flanges to about .020” puts the o-rings closer on the TDC compression stroke so again, less headspace and more of the pump volume goes into the valve.
4. Using 90D o-rings will have less extrusion and less headspace volume in the o-ring glands. Certainly this can be done for the valve o-ring but may give you an
unacceptable sliding seal on the piston… I’ve gone both ways 70D and 90D on the piston.
5. Adding more valve volume is a great idea for a long barreled 22 cal. Esp. at higher pumps. Consider that there is a maximum pressure that your pump can obtain
regardless of how many times you pump. With more valve volume you get more of each pump stroke into the valve… i.e pump efficiency doesn’t drop off as fast
because pressure rises slower.
There’s a lot more to it than that (the condensed version above), but no one wants to read 50 pages in one post… or type it for that matter :o … hth-
Wyo
If you write it, I will read it!! ;D ;D
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A 1322 with a FT, steel breech and 18" barrel can easily make 550 FPS with 10 pumps.
Not into golf, but that's par for the course, 600+ FPS is very doable depending on valve volume etc.
So what's holding your gun back?
If you want to be a high velocity player and make big power you need to call in the......Heavy Metal.
Adjustable full metal FT piston and barrel band, counterbore the valve and barrel, .154" TP.
My 1322 Medalist makes 565 FPS with an 18" barrel, steel breech, lightly modified valve, and adjustable cone piston.
It'll do over 600 FPS with a highly modified valve.
https://www.gatewaytoairguns.org/GTA/index.php?topic=185619.msg156145390#msg156145390 (https://www.gatewaytoairguns.org/GTA/index.php?topic=185619.msg156145390#msg156145390)
This 13xx used all the tricks I could throw at it minus the kitchen sink....LOL.
https://www.gatewaytoairguns.org/GTA/index.php?topic=164421.msg155834890#msg155834890 (https://www.gatewaytoairguns.org/GTA/index.php?topic=164421.msg155834890#msg155834890)
Im not sure Ron? i have studied this build in both 1377 and 1322 forms and headspace seems to be where the hold up is. i have done five builds using the same configuration and only this one has the issue. being limited in tools to make the things you guys make doesnt help, but i do the best i can with what i have. i know i need to open up the port in the barrel and use the enlarged TP, but i am leary to try it again after my first attempt on my old 10" barrel. i was able to get it over 500 FPS at 10, so i am moving in the right direction. no, lol... im not trying to take down an elephant or anything with an air gun. i would like to push this one to 550 at 10 pumps, so i am getting closer. ;)
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Thanks, guys
how did you get that pin to stick in the poppet?
I pressed the check valve onto the seat by screwing the valve together with a wooden spacer...
(https://i.imgur.com/f7LUwwG.jpg)
Now it's in the sealed configuration so I don't have to worry about tolerance issues. Drill squarely thru the inlet hole with a sharp 1/16" bit about 3/16" deep.
The hole will be slightly undersize (normal when drilling thru plastics). Follow with a drop of CA in the hole and press fit the pin.
Make sure that the pin is recessed from the face of the valve 1/16' or so as the check valve will extrude slightly under high pressure...
you don't want the piston face contacting the pin...
Wyo
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Thanks, guys
how did you get that pin to stick in the poppet?
I pressed the check valve onto the seat by screwing the valve together with a wooden spacer...
(https://i.imgur.com/f7LUwwG.jpg)
Now it's in the sealed configuration so I don't have to worry about tolerance issues. Drill squarely thru the inlet hole with a sharp 1/16" bit about 3/16" deep.
The hole will be slightly undersize (normal when drilling thru plastics). Follow with a drop of CA in the hole and press fit the pin.
Make sure that the pin is recessed from the face of the valve 1/16' or so as the check valve will extrude slightly under high pressure...
you don't want the piston face contacting the pin...
Wyo
easy enough ;). i will order the dowel pins. i do have the springs in the first pic. can i use the original valve stem or do i need to use the mrod valve stem? you show the one above as "shaped", and it looks oem, shaped how if i may ask?
what method are you using to angle relieve the port, if you dont mind?
at this point, i am willing to experiment. if i trash the gun... parts gun. i really dont have anything to lose. i will be doing the porting to the barrel as well. i will do as much of these things as i can with what i have. who knows... maybe i will get it right? either way... its solve the headspace issue or brake it down for parts to the other guns. ;)
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You don’t have to use an MRod valvestem but they are a better setup at higher pressure.
Sometimes they are finicky and don’t seal, so check it before you do all the shaping work.
Before and After:
(https://i.imgur.com/nOinwfT.jpg)
Relieving the sharp 90º port angle:
(https://i.imgur.com/53ZRUQn.jpg)
That just puts a rounded edge on the angle. It’s window-blind cord with lapping compound.
Anchor the valve and pull the cord back and forth against the sharp corner with a lot of tension.
Angling the port… this is a bit different:
(https://i.imgur.com/XnnI7LK.jpg)
That’s how I do it anyway. I’m sure there are other methods that work just as well or better.
BTW, I think your results are pretty good and if it’s easy to pump, you have a winner…
Wyo
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Thank you Wyo... awesome explanation as usual. ;D
I have it tore down. Pins will be here tomorrow then the slow and careful process begins. I'll do the valve stuff first, then port the barrel if the valve goes well.
Yep, it pumped very smooth and easy, but the headspace is something I need to solve if I can. If it is still there after all of this... ill take it as is, or strip it for parts. ;)
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Wyo kind Sir...
two more questions...
how many threads do i take off of the valve?
you put a groove in the valve stem shaft. about how long is that groove?
i dont have any 90 duro cast urethane #111's. i do have them in 70 duro, so i will go with that for the end of the valve. ;)
Thank you kindly. ;D
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Looks like you gents have the situation "well in hand".
In the meantime in the interest of advancing airgun technology, installed a 10" 22 cal barrel on the "Elephant" gun.
Used the lightly modified stock valve.
The gun mods are: (drum roll please)
Adjustable metal cone piston and brass barrel band.
Nipped the nose on the valve to match the cup seal.
Counterbored valve and barrel, ported to .150".
Duro 90 seal on the valve.
Light valve spring.
Steel breech and 10" Crosman barrel.
With 14.3 CPHPs and 22 cal 10" barrel
05 pumps 392 FPS 04.88 FPE
07 pumps 458 FPS 06.66 FPE
10 pumps 527 FPS 08.82 FPE (-38 FPS vs the 18" barrel)
12 pumps 567 FPS 10.21 FPE (-38 FPS vs the 18" barrel)
With 7.9 CPHPs and 17 cal 10" barrel
05 pumps 468 FPS 03.84 FPE
07 pumps 537 FPS 05.06 FPE
10 pumps 630 FPS 06.96 FPE
12 pumps 661 FPS 07.66 FPE
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thats very impressive for a 10" barrel Ron, but i never expect anything less in your builds. 8) ;D
oh, BTW... the pleasure dots you suggested came and i have put them in all my pumpers. i havent had a cigarette in 8 years... i almost lit one up! this is a silly cheap, silly effective way to take the noise out and it was an awesome find!!! thanks for that one! 8) ;D
the only thing i have well in hand is a mess, lol. it will be a miracle if any of this works? i had to multi purpose my drill press to do a few things it was never meant to do. the pins will be here today and i have the poppet ready. took two threads off the valve, shaped the valve stem, lighter spring, i angle ported the valve from about half way in down to where it squared off at the bottom. i havent put the groove in the valve stem yet. i ported the barrel to .156 and i may have just done that part right as it looks decent. i do not have high hopes at this point for the rest of it.
while doing the valve stuff i realized something and now i would like to know. the valve stem opens and releases the air when the hammer strikes it. there is some clearance between the valve stem and the hole it exits to on the hammer side. what keeps air from releasing through that clearance as it releases through the TP?
oh, and... what is the o-ring size for the o-ring between the two valve halves?
questions, questions, questions... ;D
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Glad to hear the PDs worked out for you.
The thick ones are the type I used.
The o-ring size is 012 between the valve halves, 111 for the main seal.
There's always a minor amount of air that escapes from around the VS, nature of the beast.
The MRod stems seem to use higher quality steel and fit tighter.
The Elephant gun with the HP valve would make another 38 FPS.
It has the 2100 nose cap and reduced valve volume, Delrin VS etc.
That would have put it around 565 FPS 10.13 FPE with 10 pumps.
Keep hammering away at your gun, it can get frustrating at times, been there, done that.....LOL
If you get to a sticking point I can make you a FT piston to try.
They're fairly easy to make and I believe that's where you'll get the most FPS/efficiency gain.
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Glad to hear the PDs worked out for you.
The thick ones are the type I used.
The o-ring size is 012 between the valve halves.
There's always a minor amount of air that escapes from around the VS, nature of the beast.
The Elephant gun with the HP valve would make another 38 FPS.
It has the 2100 nose cap and reduced valve volume, Delrin VS etc.
That would have put it at 565 FPS 10.13 FPE with 10 pumps.
for what you are already getting with a 10" barrel in .22... the stuff my dreams are made of with an 18" barrel, lol.
yeah, i ordered the PD's you linked... these things are awesome! 8)
thanks for the o-ring size... i better get some ordered. i dont have any of that size.
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here is where i am...
(https://i.imgur.com/mAp1iF0.jpg)
no awards for clean and tidy here but tried my best. i stayed with the OEM valve but did not put the groove in the stem... i am simply not clear on that one and dont want to risk creating more clearance between the valve stem and the hole it exits to the hammer from. i only have 70 duro in cast urethane but it should still be better than the buna or viton? i am limited to the derlin piston so as much as i would like to go full metal on this one, cant find them, and this is what i have to work with.
with what i was able to do, if there is still a head space issue... i honestly can say i tried everything i could to solve it. ;)
time to do a final cleaning of parts, check the barrel porting to make sure i got any interior burr removed, assemble and test it on the chrony. will post results soon. 8)
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results are in...
the arm open at 10 pumps remains the same. somewhere around 70 degrees or so. piston contact with valve, 1/2" exactly. some guns just cant be solved. nothing on this gun but the trigger assembly and steel breech is the same gun it was originally. everything related to the power plant has been changed and/or modified. was it for nothing?
nope...
14.3g Crosman super points
5 pumps - 413 / 5.4 increase of 14 FPS
10 pumps - 520 / 8.6 increase of 17 FPS
15 pumps - 579 / 10.6 increase of 29 FPS
20 pumps - 611 / 11.9 increase of 37 FPS (no retained air)
before the valve mods and barrel porting...
5 pumps - 399 / 5.1
10 pumps - 503 / 8.0
15 pumps - 550 / 9.6
20 pumps - 574 / 10.5
so it seems that the more pumps i go, the bigger the gain. i am not unhappy with this by any means. the pumping on this now is super easy and quiet. i did add a thin o-ring to the top of the TP just to be safe and that seemed to work out well. i got decent gains in FPS over what it was. i got thrown off a little because i forgot that the lighter spring means you have to cock before pumping, but quickly remembered before having a nervous breakdown, lol. so i learned how to do a few new things, got comfortable with barrel porting finally, and while a bit stressful... it was fun doing. with no more than i have to work with, i think i ended up with a decent build despite the head space issue. time to scope it and get it sighted in. hopefully... it will have good accuracy too. ;)
Wyo, Ron, and everyone who chimed in... thank you for all the help and suggestions. it is very much appreciated. ;D
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Looks like you gents have the situation "well in hand".
In the meantime in the interest of advancing airgun technology, installed a 10" 22 cal barrel on the "Elephant" gun.
Used the lightly modified stock valve.
The gun mods are: (drum roll please)
Adjustable metal cone piston and brass barrel band.
Nipped the nose on the valve to match the cup seal.
Counterbored valve and barrel, ported to .150".
Duro 90 seal on the valve.
Light valve spring.
Steel breech and 10" Crosman barrel.
With 14.3 CPHPs and 22 cal 10" barrel
05 pumps 392 FPS 04.88 FPE
07 pumps 458 FPS 06.66 FPE
10 pumps 527 FPS 08.82 FPE (-38 FPS vs the 18" barrel)
12 pumps 567 FPS 10.21 FPE (-38 FPS vs the 18" barrel)
With 7.9 CPHPs and 17 cal 10" barrel
05 pumps 468 FPS 03.84 FPE
07 pumps 537 FPS 05.06 FPE
10 pumps 630 FPS 06.96 FPE
12 pumps 661 FPS 07.66 FPE
That's smoking!! I want to do a 14" barrel on one of mine and would be thrilled with that, with the 14" barrel! What a barn gun that would make with a red dot sight!
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here is where i am...
(https://i.imgur.com/mAp1iF0.jpg)
no awards for clean and tidy here but tried my best. i stayed with the OEM valve but did not put the groove in the stem... i am simply not clear on that one and dont want to risk creating more clearance between the valve stem and the hole it exits to the hammer from. i only have 70 duro in cast urethane but it should still be better than the buna or viton? i am limited to the derlin piston so as much as i would like to go full metal on this one, cant find them, and this is what i have to work with.
with what i was able to do, if there is still a head space issue... i honestly can say i tried everything i could to solve it. ;)
time to do a final cleaning of parts, check the barrel porting to make sure i got any interior burr removed, assemble and test it on the chrony. will post results soon. 8)
Your valve job looks good.
What I see is a lot of valve volume.
Even more since you cut some threads off the valve.
I measure valve volume by how much stem travel the valve has.
Your gun has about .575", my stock valve has .385" and my HP valve has .200", about the same as a 2100 valve.
The less volume the higher pressure you'll develop at lower pumps.
The gun will be harder to pump so need to balance power with pumping effort.
The stock valve is probably the best compromise of the three.
Adjustable metal pistons are out there.
The bad news is they are pricey.
Search EBay for Crosman piston.
Here's one:
https://www.ebay.com/itm/224305229081?hash=item3439a22d19:g:m4oAAOSwUzFakaue (https://www.ebay.com/itm/224305229081?hash=item3439a22d19:g:m4oAAOSwUzFakaue)
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Looks like you gents have the situation "well in hand".
In the meantime in the interest of advancing airgun technology, installed a 10" 22 cal barrel on the "Elephant" gun.
Used the lightly modified stock valve.
The gun mods are: (drum roll please)
Adjustable metal cone piston and brass barrel band.
Nipped the nose on the valve to match the cup seal.
Counterbored valve and barrel, ported to .150".
Duro 90 seal on the valve.
Light valve spring.
Steel breech and 10" Crosman barrel.
With 14.3 CPHPs and 22 cal 10" barrel
05 pumps 392 FPS 04.88 FPE
07 pumps 458 FPS 06.66 FPE
10 pumps 527 FPS 08.82 FPE (-38 FPS vs the 18" barrel)
12 pumps 567 FPS 10.21 FPE (-38 FPS vs the 18" barrel)
With 7.9 CPHPs and 17 cal 10" barrel
05 pumps 468 FPS 03.84 FPE
07 pumps 537 FPS 05.06 FPE
10 pumps 630 FPS 06.96 FPE
12 pumps 661 FPS 07.66 FPE
That's smoking!! I want to do a 14" barrel on one of mine and would be thrilled with that, with the 14" barrel! What a barn gun that would make with a red dot sight!
Decent power for sure.
A 14" barrel would get about 550 FPS in 22 cal with that setup.
What cal would you use for your barn gun?
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Your valve job looks good.
What I see is a lot of valve volume.
Even more since you cut some threads off the valve.
I measure valve volume by how much stem travel the valve has.
Your gun has about .575", my stock valve has .385" and my HP valve has .200", about the same as a 2100 valve.
The less volume the higher pressure you'll develop at lower pumps.
The gun will be harder to pump so need to balance power with pumping effort.
The stock valve is probably the best compromise of the three.
Adjustable metal pistons are out there.
The bad news is they are pricey.
Search EBay for Crosman piston.
Here's one:
https://www.ebay.com/itm/224305229081?hash=item3439a22d19:g:m4oAAOSwUzFakaue (https://www.ebay.com/itm/224305229081?hash=item3439a22d19:g:m4oAAOSwUzFakaue)
thanks Ron ;D. i didnt reach the 550 FPS at 10 pumps like i had hoped, but it was a definite improvement over what it had before. its not what it should be for an 18" barrel, but not bad either for a .22 caliber ;). i just saw your edits in the above post and i agree. switching from a derlin piston to a metal one would benefit this gun. that FTP set in the ebay link is amazing, pricey for sure, but awesome craftsmanship put in to it. sadly, it is just too much to spend at this point. i envy you guys, lol. your understanding and ability to make your own things is almost "God like". i am grateful that you guys share that knowledge. ;D
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Looks like you gents have the situation "well in hand".
In the meantime in the interest of advancing airgun technology, installed a 10" 22 cal barrel on the "Elephant" gun.
Used the lightly modified stock valve.
The gun mods are: (drum roll please)
Adjustable metal cone piston and brass barrel band.
Nipped the nose on the valve to match the cup seal.
Counterbored valve and barrel, ported to .150".
Duro 90 seal on the valve.
Light valve spring.
Steel breech and 10" Crosman barrel.
With 14.3 CPHPs and 22 cal 10" barrel
05 pumps 392 FPS 04.88 FPE
07 pumps 458 FPS 06.66 FPE
10 pumps 527 FPS 08.82 FPE (-38 FPS vs the 18" barrel)
12 pumps 567 FPS 10.21 FPE (-38 FPS vs the 18" barrel)
With 7.9 CPHPs and 17 cal 10" barrel
05 pumps 468 FPS 03.84 FPE
07 pumps 537 FPS 05.06 FPE
10 pumps 630 FPS 06.96 FPE
12 pumps 661 FPS 07.66 FPE
That's smoking!! I want to do a 14" barrel on one of mine and would be thrilled with that, with the 14" barrel! What a barn gun that would make with a red dot sight!
Decent power for sure.
A 14" barrel would get about 550 FPS in 22 cal with that setup.
What cal would you use for your barn gun?
.22 for sure. Less chance for going thru a roof. For the distance I will shoot, I will try to find a wadcutter that shoots the best. 20yds is a long shot in a building. Wadcutters hit like a brick and don't over penetrate.
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Late to answer and it looks like you've done a very nice job, Robert, but here goes...
how many threads do i take off of the valve?
you put a groove in the valve stem shaft. about how long is that groove?
I generally leave 3 to 4 full threads so that's about half.
If you keep the turned down section of the valvestem within 5/16" of the seal...
(https://i.imgur.com/G3kNmaV.jpg)
It will be entirely within the valve port...
(https://i.imgur.com/qJ6uT3z.jpg)
So the full diameter stem will have a close-fit seal to the back of the valve... and yes the MRod stems are a better fit.
Not trying to overwhelm the topic but just expanding on the mild-to-wild theme...
This 1322 with a 12" barrel uses a retained-air system and makes 12 fpe with 8 (sea-level equivalent) pumps:
(https://i.imgur.com/oufI0gX.jpg)
It has a large volume valve, RVA for tuning, slingshot hammer, ports at .165", pinned valve (of course) and reinforced pivot:
(https://i.imgur.com/2o2WC26.jpg)
(https://i.imgur.com/gXr87Tk.jpg)
(https://i.imgur.com/oct93BA.jpg)
(https://i.imgur.com/nbU4XHZ.jpg)
(https://i.imgur.com/8tefYGi.jpg)
(https://i.imgur.com/4x3vEA8.jpg)
There's more to it than that; this rabbit hole is very deep ;D
Wyo
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thanks Wyo... i guessed at how many threads to take off based on your picture. i was close 8). i went with the original valve stem. it turned out pretty decent without the groove. i understand now why the groove, removing threads, shaping the valve stem... allows more room for air and higher volume. it definitely works! the more pumps i go, the FPS increases by really decent amounts. i havent tried this one at 25 or 30 pumps, afraid to, lol, but i can only guess with what it does below 20. 8)
that 12" gun with all the brass... BEAUTIFUL!!! ;D
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i got the pump arm angle at 10 pumps solved with Tach Driver 10's help. what ever the issue was, it was related to how the Mellon derlin piston reacted with this particular build. not sure why, but Ron sent me a custom brass adjustable piston and that solved the issue. he also sent me a hybrid 760/13xx valve to try out. i ported the barrel and used poly tube in place of the TP and got...
5 pumps - 431 FPS / 5.9 FPE
10 pumps - 571 / 10.3
15 pumps - 634 / 12.8
20 pumps - 679 / 14.6
at 6 pumps... i got 501 FPS / 8.0 FPE... perfect for my needs.
unfortunately, the project in .22 is a bust. i had hoped that this 18" Crosman barrel would have decent accuracy with a Mac1 accuracy prep, but it was pretty bad. even using H&N 14.66gr with the 5.53 head didnt help. the tolerances in this barrel are just too loose. it could hit center at 20 yards a couple here and there but overall, the shots were all over the place in about a 3" diameter range. at this point, i will keep the lower part of the gun as is, waiting for an extended probe in .177 from Mellon, and go back to my .177 14.5" LW barrel which i know is accurate.
a big thank you to Wyo and Tack Driver 10. i learned new things about how high and low valve volumes work and these are things i will use on future builds. 8)
Ron... it was very generous of you to send me the valve and custom brass piston. your machining skills are amazing and this brass piston is truly a beautiful work of art! i greatly appreciate you doing this and this gun will live to rock another caliber very soon. ;) 8)
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the conversion back to the LW 14.5" barrel in .177 is done. i used the exact same lower setup and changed only the barrel and went back to the stock probe/bolt. and the results are in...
Crosman Superpoint 7.4gr pellets
5 pumps - 508FPS / 8.6
10 - 660 / 14.5
15 - 732 / 17.8
20 - 772 / 19.9
at 20 yards / 5 pumps... just under 3/4" groups on center. that's the kind of accuracy a barrel should have, and the power... much more than i expected to get. i wish i could have kept the .22 setup, but i am very happy with the results. 8)
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That's a pretty good setup
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If that second column is FPE it would take a 15 gr pellet to get those numbers.