ORIGINAL: Semisane
If you have the Speer 50 caliber bullets (i.e. SPEER BULLETS500 S&W .500 DIA. 350GR JACKET SOFT POINT 50 PER BOX) they can not be used in a 50 caliber muzzle loader with sabots.
That is how I got my CVA Kodiak. Was at the range with my Hawken and the guy next to me asked if I could help him. He couldn't get his gun loaded. A quick look noted that he was trying to load a 50AE round into the back of the Kodiak. I told the guy what the issue was and offered to show him the right things needed to shot it. He got all PO'ed, handed me the rifle, said Merry Christmas (middle of July) and stormed out of the range.