I didn't have a chance to try a different hammer spring today, but I did try three strings, from 3000 psi, with the 78 gr. JSB pellets and two bullet weights, 127 & 154 gr.... I set the 13XX hammer spring to maximum preload, and shot 3 shots with each bullet, and the last shot was at, or just under 96% of the first.... Here are the results....As you can see, the first shot was the fastest, so adding hammer spring, while if might give a higher peak velocity, would not help create a usable shot string.... The efficiency at this power level, considering the gun is tuned for "first shot fastest" is a bit better than I expected.... With the pellets, averaging 164 FPE it was 0.69 FPE/CI, with the 127 gr. averaging 198 FPE it was 0.86 FPE/CI, and with the 154 gr. averaging 211 FPE it was 0.94 FPE/CI....I'm in a little bit of a quandary here about what to do to eliminate the fussiness of this setup to preload.... I would like to tune it for either 2 shots of equal velocity, or as flat a 3 shot string as possible.... but even small changes in preload drop the velocity a ton.... Perhaps this is a function of the heavier than normal hammer I have.... With the rear cocking rod and handle it weighs 82 grams, as opposed to 60 grams for a stock Disco hammer.... I will ponder this overnight....Bob