Small Caliber PCP Varmint Rifles

[rkr]

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.

[KnifeMaker]

Mr Bob, you're sure not doing anything to quell my desire to build a .172. 


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!!!


Mike

[Nvreloader]

Mike

+2 for me also............ , I am drooling all over the keyboard.....

Tia,
Don

[rsterne]

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

[rsterne]

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....



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....



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.... 

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

[rsterne]

I tested the .172 cal 24.7 gr. NOE HP in soap today.... It is quite spectacular at 1050 fps (60 FPE)….



The penetration was 3.5", and the wound cavity is nearly as wide as the length of the bullet, at 0.45"....

Bob

[darkcharisma]

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

[rsterne]

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.

Bob