BTW. what is that material wrapped around the piston on each side of the o-ring?

I am intrigued by your design components. I've yet to build one of these and often wondered how wood would perform as a piston. Apparently well! You have answered my question about the equalization hole in the piston. Just how big should this hole be if I use a 3" pvc coupler inside a 4" pipe? The d...

what keeps the pilot chamber air from escaping up the Tee into the barrel? I don't see how you could ever pressurize the air chamber.

I use a 40" barrel with a 1" valve and a 24" 4"sch40 chamber. Ammo is golfballs....very consistent weight and size. Almost a friction fit in the barrel. At 115PSI, generally launching 300-325 yds tops. I believe a good wadding material and/or Sabot arrangement could afford better accuracy. A fair am...