The projectile, and the damage... The CD drive was just sat up on end; when struck, it flew up and back about 5-6 feet.

do you have a lathe?, if not, how did you do the o-rings?

I turned the groves for the o-rings on a table saw. I set the saw to the depth needed, put the flat end to the fence, and rotated the piece by hand. I have used this trick many times, even just to cleanly cut 4" pipe (my chop saw's only 12 ...

You do have DWV fitting(s) on it though, so I wouldn't use it above 60 psi.

If you are referring to the bell reducer, under it is a 3" coupling with flush bushings glued inside the 4" dia pipe. It fit together very tight. Also I filled the space between the internal reducer and the bell reducer ...

Musket Specs:

Barrel: 1" bore x 34" length
Chamber: 4" ID x 15" lenght
Piston: 4" ID (3" Pipe Cap)
Pilot for piston: Rainbird CP-100
Pilot for sprinkler valve: Heavily bored Husky(Home Depot) Blowgun
Paint: TBD
Sights: TBD

The goal of this project was to build an easily portable carbine with ...

1.5" barrel: pingpong ball filled with BBs