I don't think it's AI. It's a percussion cap pistol, which is the step between flintlocks and cartridges. Barrel length seems like a normal pocket pistol length.

There are tens of thousands of gun designs, and some of them are quite goofy.

EDIT: Found it https://www.rockislandauction.com/detail/49/66/unique-single-shot-underhammer-percussion-pistol