I swapped out the tank for the other one that I had set up for 1500 psi.... I wasn't quite sure what to expect, as normally that is too much pressure for stock hammer spring preload on a QB78.... As it turns out, with the smaller plenum of the QB79, the pressure drop during the shot compensates for the extra pressure at the beginning of the shot.... allowing the stock hammer spring to work OK.... Here are the results of the Stage 2 tune running at 1500 psi....



As before, the starting pressure was 2000 psi, and the ending pressure was 1000.... I got 16 shots averaging 918 fps (26.8 FPE) down to 1400 psi before the velocity started to drop below 900 fps.... The fact that the drop in velocity starts 100 psi below the regulator setpoint indicates that this tune is operating very close to the "knee" of the curve where I like to tune my regulated guns.... The efficiency was higher than at 1200 psi, working out to 0.80 FPE/CI, and I should be able to get 42 shots @ 27 FPE on a 3000 psi fill.... That a pretty serious hunting platform....

When I did the calculations for the pressure during the shot for the 12 cc Plenum, I get 836 psi at the end of the shot, and an average pressure of 1168 psi during the shot.... That gives a pretty good indication of why the stock hammer spring preload is working so well with this setup.... It also confirms that running 1200 psi on the Stage 2 tune is running less efficiently than it could because the hammer energy is too much for the 880 psi average pressure.... I now have no doubt that reducing the preload a bit on that tune will increase the shot count with little or no velocity loss.... I'm going to have to give some thought to what is the easiest way to accomplish that, as fitting an RVA to a QB isn't the easiest thing to do, and I want it adjustable, I don't want to just clip the hammer spring....

pharoh007 - Eric, D&L, and Trailmarker are all Ninja Dealers and should be able to give you a quote and delivery....

Bob