GTA
All Springer/NP/PCP Air Gun Discussion General => "Bob and Lloyds Workshop" => Topic started by: rsterne on February 01, 2016, 08:49:15 PM
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Nearly a year ago I assembled a 7mm version of my Hayabusa PCP.... Right after that my ShoeBox compressor quit on me, and by the time I had my new Freedom 8 up and running we were busy in the Motel and I never got a chance to even shoot a shot string.... Today I rectified that situation.... First, here is the gun....
(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%207mm_zpsay9kguwt.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%207mm_zpsay9kguwt.jpg.html)
I built it on the .308/.357 version of my Hayabusa test platform, using the same valve, which ends up being full bore size porting in 7mm (.284 cal).... The tank is a 22 CI, 3000 psi unit, and the tube above it is 100 cc, with a large passage between, so the reservoir is a total of 460 cc.... The main difference with the 7mm is that I am using a barrel that is tensioned to about 1000 lb. using Belleville washers, to make it super stiff.... I intend to shoot this gun most of the time tethered to my Great White 88 CF 4500 psi tank, through a Ninja regulator modified for inline use, and set to 2900 psi.... Therefore, the first step was to determine what the maximum velocity was at that pressure, and where the knee of the curve was, so that I knew about how to adjust the preload.... Here is a graph of velocity vs. preload at 2900 psi, shooting my 96.5 gr. Bob's Boattail bullets....
(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%207mm%20Preload_zpspzyuiixz.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%207mm%20Preload_zpspzyuiixz.jpg.html)
As you can see, the gun peaks at 950 fps, which is 193 FPE, just about exactly what I was hoping for.... with the knee of the curve from 4 to 6 turns out on the preload.... I then removed the regulator from the system, filled the gun to 3000 psi, and shot some strings at various preloads to see what the shot strings were like.... I did three strings with the FN 96.5 gr., and then one with the 91.0 gr. HollowPoint version, and you can see the results below....
(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%207mm%20Shot%20Strings_zps2fi75owd.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%207mm%20Shot%20Strings_zps2fi75owd.jpg.html)
With the hammer spring preload at 4 turns out from maximum, I got five shots averaging 181 FPE ending at 2520 psi for 0.98 FPE/CI.... At 6 turns out, I got 7 shots averaging 171 FPE ending at 2420 psi for 1.07 FPE/CI.... and at 8 turns out, I got 13 shots averaging 157 FPE ending at 2060 psi for 1.21 FPE/CI.... With the Holowpoints, at 4 turns out, I got five shots averaging 179 FPE ending at 2500 psi for 0.93 FPE/CI, with the first four shots averaging 948 fps (181 FPE) within an ES of just 17 fps (1.8%).... and of course tethered it will be even tighter.... So, I can shoot on the tether at right about 1.0 FPE/CI (just fine for that use), or get 4 full power shots off tether, at 180+ FPE.... which should be just fine for hunting, as I do that from my Rhino ATV with the tank in the back....
The plan is that once the snow melts I can get some proper testing done at longer ranges.... in preparation for Varmint season in the spring....
Bob
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Very nice Bob. I'm still liking the 7mm over the .257 for some reason. The 7mm has always intrigued me. I love shooting my XP100 in 7mmBR.
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Very nice Bob. I'm still liking the 7mm over the .257 for some reason. The 7mm has always intrigued me. I love shooting my XP100 in 7mmBR.
Its a fun airgun round as well. I wish i had a little more Horse Power in my Corsair (bigger valve and a different design). But it IS a step above the 257 even though the 257 is very hard to beat. The 7mm is up there with the 308 cept the bullets have a slightly higher BC.
While BC changes, using the standard BC numbers for one of my 7mm bullets, the slug at 890-900 fps still is travelling at 470+ fps and 66 FPE at 1 mile........lol! Boy would i love to test that theory on video. Just don't have enough scope and MOA in my rig.
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everything is lookin darn good BOB.
I really can't wait to see her perform.
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I'm pretty stoked to get a solid 180 FPE on 2900 psi, even with the HPs....
Bob
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I'm pretty stoked to get a solid 180 FPE on 2900 psi, even with the HPs....
Bob
How much were you making in .357 format?
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The .308 and .357 versions used the same valve, ports (0.281"), hammer, spring, and pressure, and all had 28" barrels.... The .308 peaked at 219 FPE with 118 gr. and 188 FPE with 79.5 gr. (and 153 FPE with 50 gr. pellets at 1172 fps!).... The .357 topped out at 257 FPE with 154 gr. and 244 FPE with 127 gr. (and 198 FPE with 78 gr. pellets @ 1070 fps, with 67 gr. roundball tickling Mach 1).... Both the larger calibers, and in particular the .357, could have benefitted from larger ports....
Bob
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What ever became of your project
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Never had a chance to shoot it last summer, the Motel was too busy.... It's still hanging on the wall.... :-[
Bob
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I know the feeling, since I had to move, my compressor is not back together yet, my 4500 psi air booster is in a box in parts waiting to be rebuilt and my scuba tank is at about 2000 psi from test fire of paintball guns. I have a like new samyang 909 twin tube that has been shot one time just so I don't have to here the wife say, you bought a gun and never shot it. Lol
As soon as we find a house to buy, going to move again.
Grrrrrr I hate moving
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Nice
The main problem with 7 mm is you have to have your own molds made. Everything is around 150 gr that is made right now.
I have a 7mm barrel and I'm hoping to push 140-150 gr around a 1000 fps when I get to it.
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Yes, I did just that, Doug.... The mould was built by Veral Smith at LBT.... with the HP conversion done by Erik at Hollowpoint Mould Services....
(http://i378.photobucket.com/albums/oo221/rsterne/Bullet%20Casting/7mm%20BBT%20Mold_zpsrladqutd.jpg) (http://s378.photobucket.com/user/rsterne/media/Bullet%20Casting/7mm%20BBT%20Mold_zpsrladqutd.jpg.html)
The solids are 96.5 gr. and the HPs are 91 gr.... I can tether at 2900 psi and then get 4 good shots off tether at 180 FPE within a 2% ES.... There are so many unanswered questions with this gun.... It was the first serious attempt I made at a tensioned barrel that could be indexed, and I've never even had a chance to index the barrel, let alone play with the tensioning.... I hope that this coming spring I will get a chance to finally get that testing done, as I have a new Permission that will allow Varmint hunting (Ground Squirrels and Marmots) at ranges from 100 yards and out.... and I'm going to build a shooting bench there.... I only have one sizing die, and I need to get an assortment of bushings from NOE so that I can play with that as well....
I need another day between Saturday and Sunday every week, just for shooting.... ::)
Bob
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Never had a chance to shoot it last summer, the Motel was too busy.... It's still hanging on the wall.... :-[
Bob
Bob
Is that the monocoque you are saying is hanging on the wall or did you get the bullet molds for it and I just missed the final results for it.
I like the 7mm very much.
Mike
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Looks good Bob, really interesting to see the accuracy way out how she does. The 7mm is indeed interesting caliber for sure. Have one Hart barrel blank on my shelf waiting for a gun to put it in.
Marko
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Mike, the Monocoque is a totally different design (in fact different than anything I have ever seen for an airgun), and can be found in this thread....
http://www.gatewaytoairguns.org/GTA/index.php?topic=99759. (http://www.gatewaytoairguns.org/GTA/index.php?topic=99759.)
It is a .257 cal where the breech and barrel are both inside a full length tube, with the scope mounted on the outside of that same tube.... for the most rigid possible assembly.... It is a .257 cal, and last year was completed up to the barrel chamber.... I needed bullet moulds and a chamber reamer, and I now have the moulds, but still need the reamer.... If I don't hear from Sean Pero soon, I will be forced to make my own.... I hope to complete the Monocoque this winter, which will give me even more testing to do next summer....
The next 4 years until we close the Motel are going to be tough to find time in the summer to test.... but once that happens.... LOOK OUT !!!
Bob
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Mike, the Monocoque is a totally different design (in fact different than anything I have ever seen for an airgun), and can be found in this thread....
http://www.gatewaytoairguns.org/GTA/index.php?topic=99759. (http://www.gatewaytoairguns.org/GTA/index.php?topic=99759.)
It is a .257 cal where the breech and barrel are both inside a full length tube, with the scope mounted on the outside of that same tube.... for the most rigid possible assembly.... It is a .257 cal, and last year was completed up to the barrel chamber.... I needed bullet moulds and a chamber reamer, and I now have the moulds, but still need the reamer.... If I don't hear from Sean Pero soon, I will be forced to make my own.... I hope to complete the Monocoque this winter, which will give me even more testing to do next summer....
The next 4 years until we close the Motel are going to be tough to find time in the summer to test.... but once that happens.... LOOK OUT !!!
Bob
Thanks Bob
I just read thru the updates you posted in the thread for the monocoque and will follow with great interest and hope all goes well with the motel for the next 4 years so you can devote full time to this hobby. ;D ;D
Mike