My dad used to be a big papier-mâché enthusiast and I'd help him with his little projects when I was a little baleen. He made a ton of puppets and marionettes out of it, but he also made armor out of it, and yes it can be made to be extremely hard, dense and heavy. That is pretty beautiful work for a kid.
I was going to say "at least you have to machine the gun barrel for accurate rifling," but then he mentions that he's figured that one out and the next one will have it.