Not a Pope (no bolt on a pope), and i think Garvin is correct: Bedford Eureka, but missing the spring and retainer end-piece for the 'charging plunger' under the barrel. Don't laugh at my description (as have no idea what the actual parts would be called) - but, let's be honest, even Buck Rogers would want one of these!

Or would it be more suitable for John Carter of Mars?

Meanwhile: hands off the broken Cub Gat mentioned above (pleeeease)! Surely none of you serious collectors are going to be interested in bidding. I mean, afterall - where's the original box!