Take the ramrod and insert it fully into the barrel, and place your fingers against the muzzle so you know exactly how deep into the muzzle the ramrod fits. Then, without moving your hand on the ramrod, pull the ramrod out and place it along side the barrel to see how far down the barrel the ramrod had been once again keeping your hand even with the muzzle. If it is empty, the ramrod should go almost down even with the nipple/breach. I know with my .50 loaded with 70 grs of powder, the ramrod stops about 2 inches in front of the nipple/breach.
If it does turn out to be loaded, do NOT try to fire it, as you have no idea who loaded it with what and it may have been someone who didnt know to not load it with smokeless, so you may have a pipe bomb in your hands. Use a ball puller to pull the load and clean it as you normally would.