Before firing a flintlock musket, you have to pour a small amount of gunpowder into the pan for the flint to ignite. It is highly unlikely that any gunpowder would still be in the pan after being jostled around for 200 years.
Lamont states that he was told at gun shops that if he took the antique rifle and cleaned and polished it real good, he might get $700-$800 for it. Any reputable expert would tell you that polishing an antique gun would ruin its value, not increase it.