MAKE SURE IT IS UNLOADED!
1) Place rifle vertical.
2) Take ramrod and insert roughly 1 inch in the bore, brass end down.
3) Release ramrod, allowing it to fall into the barrel.
4) If the ramrod "Dings" it is not loaded.
If the ramrod "thuds" there is something in the breech.
5) If it has something in the breech, take it to a gunsmith and have the breech plug removed and whatever is in the barrel pushed out, and you may as well have the barrel cleaned as long as the breech plug is out anyway.
NOTE:
If the barrel is held on with wedges, it probably has a hooked breech.
Remove the wedges, **** the hammer, and lift the muzzle until the barrel unhooks from the tang and you can remove the barrel.
Soak the breech end (closed end) of the barrel in water for a couple hours or overnight to neutralize any powder.
You can then take just the barrel to the gunsmith.
If the barrel is pinned in place you'll need the correct size drift pins, a hammer, and a screwdriver to remove the barrel.
It is not unusual for an antique muzzleloader to have been loaded for however many years it hung above the fireplace mantle, or on the wall.
Stupid as it may sound/is, it is not unheard of for modern production muzzle loaders to be left loaded when put away, hung above the mantle or on the wall.
As others have said, a serial number indicates modern manufacture.