Mike
How did you measure the twist? In looking at the photos down the barrel it is hard to judge distance but If you look at the track of an individual land it seems they turnslightly more than 1/2 revolution in the distance that is visible. I have a couple of cape guns with bore gauge barrels and they are a much more moderate twist. A 12" twist is right up there with modern big bore rifles shooting jacketed bullets. I would be afraid of slippage with lead bullets of that size.
I have a Scott single 8 bore shotgun of an era just a little older than your gun. It is cylinder bore and I developed some 8 gauge ball loads for it with .835 bore size round balls (2 oz). My gun weighs a few oz. less than yours. The recoil of these relatively mild loads at shotgun velocities were not bad but firm. I know that later bore rifles operated at substantially higher velocities and used projectiles of considerably higher weight. I imagine recoil would have been pretty significant especially a light gun ( 2 to 3 pounds lighter than a double). I don't really have any idea what the loading would have been for the pinfire as to weight and velocity. I don't know if the design was for a bullet form or a ball. Many of the later German cartridges I suspect were based on ball loads and had slow twist rates to match.
