In real life, it is kinda hard to tell if a flintlock is loaded or not. You can't exactly just peer down the barrel and see if there is in fact a ball inside, as the wadding from the cartridge paper should be used to seat the ball in the barrel to prevent it from rolling out. The ram rod taps it down very tightly. That, and if there is proper amount of gap between the ammunition and barrel, the ball should not shake or rattle either.
You should, however, be able to tell if the flintlock's pan is primed with a dash of powder though, which is needed to actually spark the charge for firing.
