America is well-known around the world for being a bit too trigger-happy. Protections of the Second Amendment have allowed gun owners unprecedented abilities to buy and sell guns. It only makes sense that this would carry on to space programs. I wouldn't be surprised if an American astronaut or two had smuggled a gun aboard.
Honestly, I would not be surprised to find out that Americans had brought some sort of firearm into space. We're pretty attached to them and finding out one of them smuggled it onto the aircraft would not surprise me in anyway. If any of the countries were going to do experiment around firearms in space it would also most likely be the US.
After learning that Russians Cosmonauts carry short gun into space, I believe Americans have also being doing the same thing and maybe carrying more sophisticated weapons to the space. With all the uncertainty of whats up there and the numerous theories about the aliens, one may be forced to at least carry a weapon. You never know what you might encounter.
Yes, it would make sense for Americans to have brought firearms on board. Space was, and still is, a vast expanse of unknown. It would be a natural instinct for cosmonauts to want some form of self protection available to them. When it comes to protection firearms are a very common and natural choice. In case of an encounter with anything threatening firearms provide an easy and deadly form of protection. This is why I believe it would not be surprising if Americans had brought some form of firearms on board just like the Russian Cosmonauts.