My .54 Renegade shoots a Hornady Great Plains Bullet in 425 grains with 100 grains of 2f really well. I can get 1.5" groups at a 100 yards with them if I do my part. They are a hollow base bullet and I don't use a wad with them, just run them down right on top of the powder.
Unfortunately Hornady no longer makes these bullets except for in .50 cal. I would certainly try them in a .50 that has a 1:48 twist.
From what I've read, a 1:48 twist TC is much more picky about the bullet length than the weight. If the bullet length gets much over an inch you start having accuracy issues, in general anyway.
I've never tried a Maxi ball in mine, but Idaholewis has a video where he found that his factory barrel shot them very well if he only used lube in the narrower bottom grease groove and left that giant upper grease groove empty. The upper one holds too much lube for it to shed all of it before exiting the bore, so you wind up with lube still in some of the groove while it's trying to fly through the air. Imagine how a lop sided spinning projectile flies. I believe in Idaholewis's video the group shrank at least by half, if not more, when he left the upper groove empty. It should be noted that he used a lubed 1/8" felt wad between the powder and bullet. I believe his powder charge may have been his standard 80 grains (weighed) of Swiss 2f, but not positive on that.
I bought a decent supply of the .54 Hornady GPB's when I saw they were discontinuing them, and I shoot RB 99% of the time, but when I run out of the GPB's the first thing I'll try is a Maxi-ball with the upper groove left empty.
