Round balls are a very good load in a 50 cal. muzzle loader. Be sure the barrel twist is for round ball. One in 72 twist or that area. The TC New Englander is a 1-48 twist which is a compromise.
Why a round ball.. accuracy. If you can't hit accurately it doesn't make any difference how large the projectile is.
I have used the 50 cal. round ball for elk, deer and pronghorn. The load in my 50. cal. Green River Barrel was as I remember, 90 grain of FFF with a .495 round ball and heavy patch. I used melted Crisco for lube. This gun would shoot a 2 inch group at 100 yards, off cross sticks, with buck horn sights, when my eyes were good.
Bullet affect.. clear through a prong horn at 80 yards, both shoulders. Deer and elk stop on far side when shot behind shoulder. One bull hit on point of shoulder, drop on spot. The bullet hit spine and put right down. One cow at estimated 70 yards, facing me, bullet between shoulders into lungs, ran about 50 yards, good blood trail. Cow at 100 yards, hit behind shoulder a little high. There was no exit, bullet under skin far side. This cow went about 200 yards.
A round ball gun needs deeper groves than a slug gun. If the grooves are to deep a heavy charge may blow by patch. My Green river barrel had a choked bore, (tighter at muzzle). This barrel would loose accuracy with a 100 grain charge. I have heard that if the seal is getting blown, that the old timers would follow the powder in the loading, with about 20 grains of cream of wheat cereal. This gave a better seal.
I have shot 1 prong horn, two deer and about 8 elk with round ball guns in 50 and 54 caliber. I never wounded a animal.