GTA
All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: rsterne on February 03, 2019, 09:53:29 PM
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Last year I built two PCPs, a 6mm regulated and a .257 cal unregulated.... This year I have a .172 cal barrel for the 6mm and a .224 cal barrel for the .257.... They are both TJ's with a 14mm OD and a 9" twist, and I have the same 14mm ID x 20m OD Carbon Fibre Sleeves for them as I used on last years builds.... Here are the two rifles I am starting with.... The 6 mm is regulated at 2800 psi, with the 165 cc plenum made from 2024-T3 with a 0.095" wall, fed from a 500 cc 4500 psi Carbon Fibre bottle.... It is tuned for 125 FPE with bullets from 61-73 gr.... with a maximum of 136 FPE....allows easy adjustment of the velocity without changing the hammer strike or pressure.... Since that capability is built into the receivers, it will also be available in the two new calibers.... This means I can leave the guns tuned for the larger calibers, and just choke up the porting if necessary....
(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)
The .257 is unregulated with a MSWP of 4300 psi, but I plan to run it at 3800 psi, the same as I am currently in .257.... It has a 300 cc 2024-T3 reservoir with a 0.120" wall.... It is tuned for 165 FPE with 80-92 gr. bullets, and peaks at 201 FPE....
(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)
Both guns have my own version of the SS Valve, and MDS hammers with an 11 lb/in. spring and are very easy to cock.... They are both fitted with harmonic tuning weights on the muzzle, which I plan to fit to the new barrels as well.... The receivers are interchangeable on the lower assemblies.... If you want to read about the original builds, you can do so here.... Before you ask, I have not yet done any accuracy testing of either gun, the Motel prevents me from doing any shooting in the summer, so serious testing will have to wait until 2021, after we retire.... ::)
https://www.gatewaytoairguns.org/GTA/index.php?topic=128036. (https://www.gatewaytoairguns.org/GTA/index.php?topic=128036.)
When the new barrels are fitted I will have four calibers, and all can be shot regulated at 2800 psi or unregulated at 3800.... although I plan mostly to use the .172 regulated and the .224 unregulated.... I currently only have one bullet for each caliber, I have a HP version of the 27 gr. NOE 172-26 which weighs 24.7 gr.... and the FN version of the NOE 225-61 which weighs 61 gr.... I have already made chamber reamers and cut the chambers in the TJs barrels, you can see what that process was like in this thread....
https://www.gatewaytoairguns.org/GTA/index.php?topic=154242.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=154242.0)
Today I got a good start on fitting the new barrels.... I made two new bolts and loading trays, one in each caliber.... Here they are, along with the bullets....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Bolts%20and%20Loading%20Trays_zpsf0zwzuej.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Bolts%20and%20Loading%20Trays_zpsf0zwzuej.jpg.html)
I made the receivers with a 1/2" bore for the bolt and barrel, so it is pretty easy to change calibers by making the above parts.... The loading tray is fastened into the receiver with a single flat-head 4-40 screw.... The receiver is shown below, you can see the threaded hole for that 4-40 screw in the loading bay in the upper receiver....
(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)
The receiver is only notched out for loading on the right.... leaving the left side full height for increased rigidity.... They are both equipped with a velocity adjusting screw on the back which pushes a steel pin forward to prevent the bolt from being fully retracted in the J-slot.... This allows easy adjustment of the velocity without changing the hammer strike or pressure.... Since that capability is built into the receivers, it will also be available in the two new calibers.... This means I can leave the guns tuned for the larger calibers, and just choke up the porting if I have too much power.... The next step will be to machine the barrels to fit the receivers, and machine the barrel ports, transfer port recesses, and grooves for the O-rings to seal the breech....
Bob
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Subscribed. I can't wait to see the .17 velocity results.
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Beautiful, I love the contrast between the tacticool M4 stocks and the traditional Crosman grips.
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I'm not in love with "tactical" style rifles, I prefer wood.... but they sure make life easy when you are developing ideas you want to be easily interchangeable.... The Crosman PRod triggers and grips are a inexpensive way to get a great trigger assembly....
Bob
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Your builds have definitely inspired me. I wish I had your skills and the equipment to put them to work. But, since I don't I had this one built. It's a Cothran Powerhouse valved .30. I'm working on tuning it for the Accurate 30-075A slugs.
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they sure make life easy when you are developing ideas you want to be easily interchangeable...
Exactly why the AR system has become so ubiquitous in the powderburning world, no surprise that some of it would translate to airguns.
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Today I worked on the breech end of the barrels.... First I machined the O-ring grooves, checking as I went to make sure I got the groove the proper depth to get a nice sliding fit on the bolt.... I used a #009 O-ring on the .224 cal and a 4 mm ID x 6.4 mm OD x 1.2 mm CS O-ring on the .172 cal.... I had to grind down the internal grooving tool I had made previously for that CS Metric O-ring as it was too large in diameter to fit inside the tiny bore.... These were time-consuming to make, but went well and I am pleased with the results....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Barrel%20Ports%20and%20O-ring%20Grooves_zpsllqhtnbm.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Barrel%20Ports%20and%20O-ring%20Grooves_zpsllqhtnbm.jpg.html)
I also laid out and machined the barrel ports and the 3/8" flats for the transfer ports to seal against.... Both barrel ports are oblong to get full bore area without exceeding 80% of the caliber for the width of the port.... The .224 cal port is 0.176" wide and 0.27" long, and the .172 cal port is 0.136" wide and 0.26" long at the boreline…. Both start at 0.257" at the transfer port face, to match up to the transfer port ID, and are blended from round to oblong within the thickness of the barrel wall....
This was a long day requiring a lot of concentration, so I am putting off threading the muzzle end for the harmonic tuners for another day.... Once that is done I will be able to cut the carbon fibre sleeves to length and glue them onto the barrels.... This project is moving along quite nicely.... 8)
Bob
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Hey Garry, nice job... 8)
Keep up the good work....
Bob
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Today I threaded the muzzles 1/2"-20 NF to accept my harmonic tuners.... I can also use a Hatsan Air Stripper, should they become available again.... I then cut the Carbon Fibre sleeves to length.... They are 14mm ID x 20mm OD, so once installed the barrel will be over 3/4" OD.... I sanded and cleaned the barrels and the inside of the sleeves, and installed them with Loctite 638.... Here is what the muzzle looks like, without the tuner in place....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Muzzle%20Threads%20and%20CF%20Sleeves_zpskl44uhan.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Muzzle%20Threads%20and%20CF%20Sleeves_zpskl44uhan.jpg.html)
After an overnight cure at room temperature, I will give them a post cure in my wife's oven at 175*F for 3 hours.... Then I can finish fitting the OD of the sleeve to the receiver and drill the 6 holes through each sleeve for the setscrews so that they bite against the steel of the barrel when installed....
Bob
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I’m subscribing. I’m very curious to see how your .172 does. I’ve been thinking about trying to build up a .172 for grouse but got sidetracked with .172 powder burners.
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Is there a benefit to the carbon fiber sleeve beyond aesthetics? Does it stiffen the barrel for better accuracy?
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The primary reason for the carbon fibre sleeve is to stiffen the barrel and improve accuracy by reducing the amplitude of barrel vibration during the shot cycle.... I will further tune out any remaining vibration with the harmonic tuner on the muzzle, which is a movable weight that will allow me to have the bullet exit from the muzzle coincide with the momentary pause of the barrel at the end of a vibration, by tuning the frequency at which the barrel vibrates....
For those who don't know about carbon fibre, it has approximately the same strength and stiffness as steel, but weighs about 1/6th the weight of steel.... The sleeves I am using on this gun are 20mm OD, while the barrel was only 14mm.... This increases the stiffness of the barrel by over 4 times.... The 28" long steel .22 cal barrel weighed 26 oz.... and the carbon sleeve weighs only 5.7 oz., for a total weight of 1.98 lbs.... If I had a steel barrel that was 20mm OD, it would weigh 3.65 lbs.... so I have saved 1.67 lbs. in weight compared to an all steel barrel of similar stiffness....
If you are building a bench rest gun, where weight is an advantage, then use an all steel barrel.... For these guns, where I used an aluminum tube to save weight, sleeving the barrel with carbon fibre is the way to go, IMO.... plus, as you say, it does look cool.... ;)
Incidently, when I was purchasing this CF tubing, I found that the manufacturer makes a 20mm ID x 30mm OD tube that would slide over the one I have.... That would increase the stiffness by 5 times over what I have now, or more than 20 times as stiff as the steel barrel alone.... yet add less than 1 lb. more weight.... Of course you would have to incorporate the receiver into the outer tube (by building it into a 20mm OD structure), like I did in my Monocoque PCP.... but what an amazing way to build a light, rigid structure.... 8)
(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/Monocoque%20PCP%20on%20BiPod_zpsdff5kkmo.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/Monocoque%20PCP%20on%20BiPod_zpsdff5kkmo.jpg.html)
You can view the thread about that project here.... https://www.gatewaytoairguns.org/GTA/index.php?topic=99759. (https://www.gatewaytoairguns.org/GTA/index.php?topic=99759.)
Bob
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The primary reason for the carbon fibre sleeve is to stiffen the barrel and improve accuracy by reducing the amplitude of barrel vibration during the shot cycle.... I will further tune out any remaining vibration with the harmonic tuner on the muzzle, which is a movable weight that will allow me to have the bullet exit from the muzzle coincide with the momentary pause of the barrel at the end of a vibration, by tuning the frequency at which the barrel vibrates.
Thanks for clarifying :)
I'm familiar with the tuning part, here's a brass muzzle weight I had machined for a friend's CZ .22 Rimfire, I went a little fancy with a threaded adjustment:
(https://i.imgur.com/M8KI8iQ.jpg)
(https://i.imgur.com/kZjan4F.jpg)
(https://i.imgur.com/11x9dGa.jpg)
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Harmonic muzzle tuners are common in rimfire shooting, because you have to tune the gun to the ammo velocity, much like with an airgun…. In centerfire they are less common, because you can tune the load (powder weight) to give the best velocity to match the harmonics of your barrel.... Some guys do use them in centerfire, of course....
Bob
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Bob,
Would I be correct in thinking that a CF bonded to the steel barrel would also have better inherent damping than a steel barrel of equivalent stiffness?
Perhaps this does not matter too much, if the projectile gets to the muzzle on the first or second oscillation. If it took the pellet several barrel wags to get out the muzzle, then both reducing the initial amplitude and increasing the rate of decay would help.
Of course, a stiffer barrel does not deflect as far, but it rings at a higher frequency. Adding a mass at the muzzle would bring that frequency back down again; making "timing" the pellet exit easier...
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It's possible that the dissimilar materials may have a superior damping effect.... You are correct that a stiffer barrel has less amplitude but a higher resonant frequency, and indeed the tuner mass would lower that.... I don't think finding a "node" should be a problem with our relatively low velocities....
Bob
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I don't think finding a "node" should be a problem with our relatively low velocities....
My logic suggests PCP airguns have so little recoil and vibration that this is a theoretical precept. Then, I watch through-the-camera scope footage and am surprised by how much the barrel waggles relative to the scope after the shot...
Yes, the scope and perhaps more pointedly, the camera mounts are probably where the flex is happening. But, the event seems much more "violent" than watching from the side would suggest.
Then again; free floated long barrels of perhaps 1/2" diameter, are gong to flex very easily. All you have to do, it lightly touch them near the muzzle to see how "softly sprung" they actually are...
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I remember a couple decades ago, Browning came out with this idea of the removable muzzle weight commercially. It was called the BOSS. And it worked!
In the late 80's and early 90's, I was part owner of an Archery shop. When the manufacturer contacted us about the limb savers, I was skeptical. I tested many bows with it, and again, It worked.
Cedric and I discussed the possibilities of trying them on barrels. Again, they worked. ;)
We also tried what we thought was a novel idea in the shop. I made some bow balance weights from PVC, filled with lead shot and oil. Man, Now they are sold commercially. GRRRRR!!! Everyone at 3D matches wanted to try My idea. The archery industry caught on, and the rest is history.
I've done this a lot, and have seem many of my original ideas incorporated into different fields. Never Made a cent on it, nor did I try to. But it feel good to know what I have accomplished. Others were the polished pistons in the Shoebox compressors,and the hardened M-2 high speed steel construction. (Mr. Bob will be familiar with it as high quality end mills) are very popular in it. Not to mention ultra edge holding in Knife Blades!
And a new, yet unnamed nano tech oil Being tested here at Ft. Hood Texas. I tested it for lubing pellets and bores for BR powder burners. It later became available as FP-10 oil and now owned by Shooters Choice.
Oop', I didn't mean to thread jack. I just get so carried away with innovation. would love to be able to make a balanced valve. Man, I need a lathe to go with the mill! Mr Bob Loyd, and Travis really impress me with the things they do. ;)
I have two barrels here that need o rings fitted. Again, no lathe. I told Travis I was using industrial 1/4 shrink wrap on the probe and it is holding up fine. He was intrigued with that. Makes testing easy. Just can't use if to magazines. GRRRRR!!
Knife
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Innovation is what this sport is all about.... I'm glad there are a few people who willingly share their ideas for the betterment of all instead of hoarding them with the faint hope of getting paid for them....
Bob
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Yesterday I did a post-cure on my barrel sleeves, crowned the muzzles, and lapped the bores with JB Bore Paste and then polished them with Bore Brite.... Today I turned down the breech end of the sleeves a few thou to fit into the receivers.... Once that was done, and the barrels could be slid into place, I marked and drilled the locations for the six setscrews in each barrel, fitting the .224 cal. barrel to the .257 receiver and the .172 cal. barrel to the 6mm receiver.... I use a SHCS drilled though with a 1/8" hole for a drill guide, which I install in each hole and then run the drill down to drill through the sleeve to the barrel....
(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)
After marking all six holes, I then enlarge the holes with a 3/16" drill, removing all the CF to that diameter and leaving a shallow pocket in the steel of the barrel for the setscrew to bite into.... Here is what the finished barrels look like....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Finshed%20Sleeves%20and%20Ports_zps38sbitkv.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Finshed%20Sleeves%20and%20Ports_zps38sbitkv.jpg.html)
You will notice that the O-rings are in place in the groove in the breech end of each barrel.... I checked the length of each bolt nose when retracted into the J-slot, and shortened them flush with the back of the barrel port.... They load the base of the bullet just past the front of the barrel port, then you pull it back into the lower slot to remove all obstruction to flow.... That retraction distance can be decreased with the velocity adjusting screw on the back to force the bolt nose to partially obstruct the barrel port....
After lunch, I checked everything over and fitted the .172 cal upper to the regulated lower.... The transfer port was the proper length, so I was able to take a few shots.... I didn't change the SSG adjustment from the last time I shot the 6mm, and by measurement it was set at 8 turns of gap.... Even so, those tiny 24.7 gr. bullets screamed across the Chrony at 1060-1070 fps.... What really shocked me was how quiet the gun was.... Mind you, the last few times I tested in the shop I was shooting a .357, but even so, the report was very low.... Not what you would get with some assistance from a can or shroud.... but they are illegal in Canada anyways....
I then removed the .172 cal upper and fitted the .224 cal one.... Once again, the existing transfer port length was fine, so a took a few shots.... With the 61 gr. bullets I intend to shoot in the unregulated version the velocity was only 775 fps.... so I tried some of the 47.6 gr. Bowmans and they shot a very respectable 930 fps at the 2800 psi regulator setting I am using on this lower assembly.... That's a bit less than I was getting in my .224 cal Hayabusa with the same bullets, but that was shooting at 3000 psi.... and as I said, I never even touched the SSG gap, it was still set for whatever tune I last had for the 6mm.... The .224 was noticeably louder than the .172.... so I guess it really was that quiet.... 8)
I have a leak to chase down in the unregulated lower assembly, it was empty when I pulled the .257 upper assembly off.... The bottle on the regulated lower assembly, on the other hand, was still sitting at 3600 psi, which is about where it would have been when I put it away months ago.... In fact, I never added any air to it for todays initial testing.... I am delighted with todays results, and over the next few days I will do some proper testing to explore both the upper power limits and the efficiency of both the .172 cal. and .224 cal. uppers on the 2800 psi regulated lower assembly.... Testing the .224 (and probably the .172 as well) at 3800 psi unregulated will have to wait until I find and fix that leak.... ::)
Bob
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I got 970 fps with those .224 Bowmans from a 24" barrel, 2700 psi reg and BSA valve system originally intended for 12 fpe guns - you should easily breach 1000 fps mark with them if you up the power a bit.
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Mr Bob, you're sure not doing anything to quell my desire to build a .172. ;D
In fact quite the opposite. Only worry is the crazy Winds we get here in Central texas. However, the BC's can be quite good, soooo!!! 8)
Mike
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Mike
+2 for me also............ 8), I am drooling all over the keyboard.....
Tia,
Don
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I was able to push the .224 Bowmans to 1035 fps in my Hayabusa…. but the air use was crazy for only 113 FPE.... I backed the velocity down to the mid 900s and used about 1/2 of the air.... I assume this gun will do similar, I should find out in the next few days...
I wish there was more available in .172 cal moulds…. I have the 24 and 26 gr. NOE moulds (the 24 gr. is a shortened 26 gr. without gas check stub)…. but it looks like I could use something heavier.... Either that or I can back the setpoint pressure down.... or use the velocity screw to choke off the barrel port....
Bob
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I tested both barrels today, first on the regulated lower at 2800 psi, and then on the unregulated lower, tethered at 3800 psi.... First, are the results regulated....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Small%20PCPs%202800%20psi_zps4eyya79a.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Small%20PCPs%202800%20psi_zps4eyya79a.jpg.html)
The .172 cal HP maxed out at 1060 fps (61.6 FPE), and at this pressure I was not really able to dial the velocity down much.... With 8 turns of SSG gap it was still shooting 1050 fps, but it only used 300 psi from the 500 cc (30.5 CI) bottle for 10 shots, ie just 30 psi per shot.... That should mean between 50-60 shots per fill.... I can dial the velocity down by using the velocity screw on the back of the receiver.... Screwing that in 6 turns drops the velocity to 980 fps....
I used a 45.0 gr. bullet when testing the .224 cal at this pressure.... It maxed out at 1010 fps (102 FPE)…. This was more out of curiousity, because the intended use of that barrel is with a heavier bullet in the unregulated version at 3800 psi.... Here are the results at that pressure....
(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Small%20PCPs%203800%20psi_zpsfs2oqref.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Small%20PCPs%203800%20psi_zpsfs2oqref.jpg.html)
As you can see, with the 61 gr. bullet the gun peaked at 997 fps (135 FPE), and had a normal tuning range of about 200 fps, as can be expected with an SS valve operating within its design range.... At 6 turns of gap, the velocity was 960 fps, and 5 shots averaging 125 FPE used 400 psi from the 300 cc (18.3 CI) reservoir, which works out to 1.24 FPE/CI.... This gave a short string starting from 3800 psi, with the first 4 shots within 11 fps, dropping another 11 fps on the 5th shot (less than a 3% ES)…. This means I can tether at 3800 psi and expect that kind of performance with the tether removed, which is just about perfect for my use....
I tested the .172 cal upper, just out of curiousity, at 3800 psi, and it was just shy of 1200 fps.... peaking at 1184 fps (77 FPE)…. Dialed back to the minimum practical with this valve, it was barely subsonic, at 1120 fps.... :o
So, this project ended up right where I wanted it for the .224 cal version.... The .172 cal is maybe a bit hot, I'll have to see how it shoots at 1050 fps, compared with dialed down a bit with the velocity adjuster.... If it ends up shooting better in the mid 900s, then it would be best to reduce the setpoint pressure, but since the regulated lower is shared with the 6mm barrel, and that shoots right where I want it at 2800 psi, I will just dial the velocity down by restricting the barrel port with the velocity adjuster if necessary....
I am delighted with the way this project turned out.... I now have 4 calibers interchangeable between the 2800 psi regulated lower and the 3800 psi unregulated lower.... I hope they end up as accurate as they are powerful....
Bob
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I tested the .172 cal 24.7 gr. NOE HP in soap today.... It is quite spectacular at 1050 fps (60 FPE)….
(http://i378.photobucket.com/albums/oo221/rsterne/Ballistics/172%20cal%20HP%20at%201050%20fps_zpscgg11hoq.jpg) (http://s378.photobucket.com/user/rsterne/media/Ballistics/172%20cal%20HP%20at%201050%20fps_zpscgg11hoq.jpg.html)
The penetration was 3.5", and the wound cavity is nearly as wide as the length of the bullet, at 0.45"....
Bob
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hi Bob. Would you shine some light on the dimensions of the tubes you used? I am interested in using that same material to build something similar. Some details about safety is very nice. I can always absorb some safety tips
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As I linked in the first post in this thread, the original build from last winter can be found here, with all the details....
https://www.gatewaytoairguns.org/GTA/index.php?topic=128036. (https://www.gatewaytoairguns.org/GTA/index.php?topic=128036.)
Bob