If you have a sign on, try asking over on cast boolits.
It could be a rechamber of a gun imported with the barrel cut back or an entirely different barrel swapped in.
I see similar project cast bullet rifle projects over there. They have a single shot sub forum. I would look and ask there.
Neat gun, I am more a low wall guy. Would love a light rifle in 25-20 but my eyesight kind of has leaning away from old style iron sights.
It reminds me the short Winchester trapper model low 1885s that CDNN was surplussing for several years. The short barrel big caliber versions languished forever until recently. Miroku made but well built. I wish they made a few more variants of the 1885 again. I have a Taylor Arms/Uberti in .38-55 that is cool but not my ideal, long heavy barrel, straight grip stock and the crescent butt. Would much prefer a lighter barrel, full or half pistol grip shape prince of wales i think is close, basically like the old winchester and browning shotgun grips, and a flat or slightly curved shotgun style butt pad instead of the deep crescents.