This is an interesting discussion for me. I have never been involved with antique guns or black powder shooting. I have shot some modern muzzle loaders but that's the extent of it. I had no idea that antique weapons were treated any different than any other weapon.
I am not sure that at the end of the day it makes any real difference. If you carried a "not a gun" into an establishment or area where concealed weapons were prohibited and were found to have it I'm afraid you would have some trouble convincing the park ranger/security officer/local LEO that it wasn't really a gun. If you unholstered your "not a gun" or used it in this situation, convincing a judge or jury that it was "not a gun" seems unlikely. Being alive to face charges or defend yourself in a law suit might be the upside.
