
1.5L aluminum chamber.
QEV slightly modified.
6feet 3/4" as main barrel, definitely packs the biggest punch energy wise. I also have 3.5feet and 8feet 1/2" barrels, I only shot the 8feet barrel twice since I haven't got a breech loading system yet nor an 8feet ramrod.
The small ball valve is to minimize the pilot volume before firing and makes it possible to disconnect the pump without triggering the gun.
At the moment I mainly fire spuds. Batteries or cylindrical bearings at close range if I want damage. And my own home made projectiles made by making an arrow out of soda bottle labels with a screw in the tip

I'm going to shoot some marbles soon.
I still have a huuuuuge To-Do list tho, I'll update when I get the following done:
-Measure projectile velocities using laser gates from college
-Damage pics
-Mount green laser pen onto it (10mW green, so the laser 'll draw a clearly visible line through the air at night

Next up would be creating my own piston valve, use the oxygen bottle, 10feet+ barrel, over 1000psi and a mounting for the whole thing (hehe ambitious
