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