Wish I could handle it, makes me wonder if a type of breech loading system.
I'm thinking along the same lines as Phil... Maybe some kind of breechloading mechanism for loose powder and ball. The little crank handle on the drum cover suggests it is made to be removed and replaced frequently, possibly for every shot. I'm wondering if it might be something like an upside-down Ferguson rifle but with percussion ignition. It appears the powder chamber is small, but the rifle is only .32 caliber, so a heavy powder charge would not be necessary. Maybe an experimental rook rifle, or something along that line.
I'm hoping some of our British and Continental friends will contribute their thoughts.
Notchy Bob