2560 HPA Velocity vs. Air Use

I finally got my 2560 assembled today, running on a 17 CI tank (it was advertised at 18, but I actually measured it at 280 cc = 17 CI) regulated at 1600 psi.... I used 10 shot strings of three different pellets at each hammer spring preload and recorded the total psi drop, which allowed me to calculate the volume of HPA used per shot.... I then graphed the velocity at each setting vs. the volume of air released by the valve as follows:

http://i378.photobucket.com/albums/o...tyvsVolume.jpg

There is a big jump in air consumption at the final hammer setting, as those shots resulted in the valve still being open when the pellet left the muzzle.... The increase in muzzle blast was significant.... You will note that the plateaus which indicate very little additional velocity gain is taking place start at about 10 cc for the Lasers, 12 cc for the Kings, and 14 cc for the EJ Points.... That is consistent with other data I have from many guns that indicates that heavier pellets can stand a bit more preload at a given pressure before "hitting the wall".... Since the volume of the barrel (23.5" long from the transfer port to the muzzle) is 18.9 cc, I was also able to plot the velocity vs. the position of valve closure as follows:

http://i378.photobucket.com/albums/o...vsPosition.jpg

This places the point at which very little velocity is gained at about 53% of the distance from the breech to the muzzle for the Lasers (at 1080 fps), 63% for the Kings (at 965 fps), and 74% for the EunJins (at 815 fps).... I'm sure that those values will provide for an interesting discussion.... but they are not inconsistent with data I have from numerous other guns....

Bob