It's double barrel!!
That hammer can apparently be flipped over to the second barrel. It looks like it might even have a sort of safety, where the hammer can be pushed out of alignment with either primer.
I'm really curious about the trigger mechanism - it looks as if it may have a sort of sear, although maybe the sear is just the trigger finger. But, heck, this is not at all bad. A little polishing and stain, and it'd be downright steampunk.
Absolutely no sights. There's a big coin glued to the back of that huge hammer, which obscures any potential sight picture, but given the barrels are likely smooth-bore, accuracy is in any case probably limited to point-blank range.
Pretty snazzy, for a meth-head.
Edit: I'm going to revise my estimate of this thing. In one picture, the hammer doesn't block the view over the barrel, so I think this might be single action, which would be crazy and more complicated. But I'll be darned if it doesn't look cocked in one picture. Which would make aiming possible. Plus there's some mechanism on the far side interacting with the trigger which might be functioning as the sear. This thing is wack! It needs to go to a museum, and not be destroyed. Better yet, give it to Ian and let him do a video.