Well, now that it's been revived: I'm curious how you adapted the muzzle-loader barrel to the plumbing fittings. Is the barrel threaded NPT? I bored out the straight breech plug threads, slipped a 1/2" pipe into the hole and ran a small weld bead around the pipe. If you can't weld you could bore a ...

I made a few corrections to the parts list for this cannon

Yes! Yess!
when i am not video recording or testing i use the 20oz co2 and high pressure stabilizer set at 400 psig for shooting. The setup in my 1st pic above.

A spring in the magazine just adds more difficulty in constructing the gun since you would need a heavy spring to push the 3/4 lb of lead that 28 balls makes up. You would also need a very long spring and several inches longer magazine tube. I am trying to make it as simple and reliable as possible....

This one will be flat black when all the painting is complete.

The annular space around the bolt is so small I had to sand the bolt down for a smooth fit and the stainless steel tee has a smooth and consistent diameter throughout. Also the volume of air in the chamber overwhelms the tiny amount of leakage around the bolt. I actually shot a single shot with the ...

The air chamber on this gun is only 1-1/4" diameter by 10" long.
It is shrouded with 1-1/2" PVC to give it more comfort against the
cheek when using CO2.

Homemade totally off the shelf re-purposed muzzleloader. It's being fired with 250 to 300 psi air from a good quality 250 psi stirrup pump or my re-purposed 30# propane tank with pod pop-off protection at 315 psi. The 300 psi air is obtained by piggybacking an R-22 compressor onto a 120 psi shop air...

Thanks everyone for the good advice and compliments

The receiver of this gun was made by taking a 3/8" compression Tee and inserting a tubing to male npt adapter into the leg of the Tee. Cinch tha leg compression nut down tight and turn it so that one of the flats is facing the muzzle. Chuck the Tee into a vise and drill a 3/8" hole through that flat...

The magazine of this gun is simply a piece of scrap cpvc 1/2" dia by 7-1/4 in long. The cap is a 1/2" copper tube cap. Once the end of the cpvc tube is capped a 3/8" hole is drilled in the center of one side all the way through the side of the cpvc. so that when this cap is turned 90 degrees the hol...

This is my 36 caliber QEV gun. I chose .360 #000 buckshot for the ammo. The Barrel is a 3/8 inch hydraulic brake seamless ss tube shrouded with a pvc pipe and tipped with a muzzle brake. The ss tubing is stiffened by wrapping 3 rubber tape bushings around the barrel to get a nice fit inside the pvc ...

Thanks Man.
Also thanks for all the other comments
by others that I missed.

During the initial construction of this gun, I only had my shop air compressor with 120 psig air and a .35 liter tank. The larger tank gave me better performance. When I got my 250 psig stirrup pump I reduced the size by 40% and still got very good performance. Now that I have 300 psig available I l...

All the parts for this cannon are totally off the shelf starting with the re-purposed 50 caliber muzzleloader barrel. I am presently firing it with 250 to 300 psi air from a good quality 250 psi stirrup pump or my re-purposed 30# propane tank with pod pop-off protection at 315 psi. The 300 psi air i...