Knew a couple homebrewers who were going to attempt them. If you want an expensive piece of history, hey that's your thing so enjoy it, then go ahead and get one.
One homebrewer and I were trading notes, hadn't started any builds, and we noticed that for not much more you could build a free shooting recoil platform that had an open breach, would probably lose a ton of pressure and velocity. Guy had done a single shot loader model of a .22lr and it still chronographyed very high, and all you needed was to pop in another round, while your thumb held the bolt back(maybe a pound of resistance) maybe a centimeter he told me. He had it for a bit before he destroyed it, for reasons that were his own, he could hit soda cans out to ten yards with the three inch barrel he had on it, but I never saw it in action so I don't know. His notes looked doable though, even if they could be improved on, probably why he destroyed it, the guy was a perfectionist, even built himself a wheelock pistol from scratch.
Personally I'd get some steel piping, or galvanized iron piping, or a dowling rod if the gun was meant to be a throw away. The action looks simple enough, a single-action with trigger release, pressure applied to a block that allows the action to move striking the primer. Could probably make the striking mechanism from one solid chunk of metal, or cut a flat after appropriate bending, to use a hardened steel nail for a striker that you arc weld into the flat. Granted it looks like a milled action, but a stamped one could still be rather effective with modern metallurgy and tech. You'd need a ton press likely for the precision of bending but a sledge hammer could get you far enough if you've got a good eye and kiln, or at the very least a MAPP gas torch to heat the flat cherry red, to harden it you'd probably consider some engine oil to cool it in. But that's all theoretical, and I'm still finishing up a PPSH43(need to use a lathe to make some trunnions) build, and am going into exams.
