Ok guys - You won't get any noticable expansion out of any bullet shot out of a muzzleloader unless you hit something solid like a shoulder joint. But then you probably won't get the penetration. The MV of the muzzleloader is just too slow to allow for expansion. I've shot Hornady XTP bullets out of my .44 mag and muzzleloader. These expand out of the .44 (with full house loads), but not out of the ML.
Don't expect a deer to drop where it stands with a ML unless you hit the spine. It may happen occasionally but its not the norm. With a double lung hit from a .50 cal ML, you should find your deer within 100 yds.
I shoot 245 gr Powerbelts out of my ML because they are the most accurate I've found.