Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:4790445.

My remix of https://www.thingiverse.com/thing:4713483.

Hardware you will need. Listing McMaster-Carr parts #s

will need one of these for the breech - Oil-Resistant Buna-N O-Ring 1/16 Fractional Width, Dash Number 012 9452K21

and 6 of these but I'm sure there's a ton of other screws that will work - Steel Phillips Flat Head Screw 82 Degree Countersink Angle, 4-40 Thread Size, 3/8" Long 90273A108

And finally, you will need a length of 17/32" brass barrel. to stick in Mega_Inline_Brass_4rd.stl. The brass should seat 1cm in the part and glue if needed. I used 2.5" of brass but haven't tested what is most efficient. Getting 75 - 100 fps.

Build includes this Picatinny hand stop: https://www.thingiverse.com/thing:4154584

Grip cover -https://www.thingiverse.com/thing:4322754

and a couple of remixes https://www.thingiverse.com/thing:4790443 https://www.thingiverse.com/thing:4790442