Looks a lot like a Marlin SS guide gun withe forend broken off and the muzzle taped. Looks like it's lead a hard life. I used to pack a sawed off(legal length) single shot in the canoe camping and running traplines. I'd pop the barrel off and use it as a billy to finish critters in a trap. It would wallow around in the bottom of the canoe and get propped up by the fire or stove to dry out. I put more than a few ducks and geese in the pot with it.m

After the first shot the rest are just noise.