RE: .50 or .54??
A 54 can do quite well with a PRB at 50 yards and will shoot a 300 gr jacketed or unjacketed 50 cal pistol bullet in a purple 54 /50 sabot or you can use a 54/45 0r 44 sabot andsabot or the 54 real bullet or the 54 Maxie ball, I also use the buffalo bullet.
The Bull Shop andNo Excuse bullets or the new Hornady FPB which is the easy one to get to shoot good as most guns like it.
I personally like the PRB in a traditional gun, and nothing else gives the long range performance that a 54 with 110 or 120 gr of powder will with a patch round ball.
Lee