Not sure if it's a dummy round, a display case, or a rimfire..........did they ever make 45/70's in rimfire? I'm betting it's just a dummy/test round. Looks like a Remington 350-grain HP in there. Shaking tells me there's no powder inside, unless it's black powder, and compressed. But I don't think so. 70 grains of BP is only 1/100th of a pound, but it seems too light to have powder in it.