Built this many years ago, at least 7 or 8 years ago with my brother. Got the tubing from a steel shop and had them weld in a plug. We of course did the drilling for the 6-1mm #11 nipple. And then used a frame off an old log splitter that blew up. Welded up some support bars and made a hammer with a spring to fire the cap off. We later added the shield to it. Its pretty fun to take out shooting. I havent made a lead slug mold for it yet so we basically just wad up foil, a wood plug and either shoot that or add some ball bearings. I once loaded it up with BB shot and set up a target 60 yards away, wow! Talk about the ultimate shot gun LOL.
The original load was 350 grains pyrodex RS. If you think shooting a muzzle loader is expensive, upgrade to a cannon
Caliber is 30mm