Back on topic, The videos are great. Have you tried higher pressure? I like the idea of the 1/2 tennis ball. I may try one to see how well it holds up.
Haven't tried that high pressure yet, only 60. It is really loud and I might be making the neighbors angry. Maybe I'll try it in the backyard or something, but not today, the storm is causing terential downpour so not much shooting done today. The piston face is blowing out also because I forgot to buy a washer big enough for the front when I was getting parts so I just threw a smaller one on for testing. I will get a new one soon though so I can test it more. The tennis ball is doing very well, especially for such a large piston.
Do you think the force on the piston will become too strong for the bumper when the pressure is higher and a barrel and projectile is used?
I think it will be fine, but if the back plug breaks I can just replace it with a metal one... then it won't break again. Can you explain how the piston will be under more force with a barrel and projectile?
Also today I realized that the piston doesn't move back much from the seat, less than half an inch, so I will cut some of the threaded rod off so I can get some better flow.