You don't mention what you're hunting. I don't believe that the bullets marketed for muzzleloaders have sufficient sectional density (s.d.) for elk. I've had too many elk run off with no blood trail. Even with a heart shot at 90 yards there was no blood trail. I have a Kahnke rifle, which shoots the Barnes 290 gr. very well, and the 340 gr. Precision Rifle bullets very well. Either one of these bullets will usually drop a deer in its tracks. Both are expensive bullets. I go for heavy for caliber bullets every time. If the bullet doesn't perform well, the s.d. makes up for a lot.
I started playing around with Harvester Crush Rib sabots and 45-70 bullets. I got some Remington .458 dia. 405 gr. Hollow Points from Outlaw State bullets and shot a one hole group at 100 yards with 115 grs. of Pyrodex. I shot an elk at 220 yards, and hit her in the spine. I was aiming at that height, but in the excitement of the hunt I forgot about the wind, which was significant. I hit about 12" behind the shoulder. It was an DRT shot. The quickest kill I've ever gotten on an elk. I found the bullet and jacket under the hide on the far side and another 8" back. It had expanded from 3/4" to 1".
I've been reading the The Buffalo Harvest by Frank H. Mayer with Charles B. Roth, and they were dropping buffalo at 300 yards using 120 grains of powder and 550 gr. bullets. I can tell you that the 405 gr. bullets with 115 gr. of Pyrodex doesn't kick as bad as lighter bullets with 150 gr. of 777. I use a couple of shoulder pads at the range, because I found I started flinching with heavier loads if I didn't. I denied it for years, but recoil affects everyone. I bought a scope that compensates for the drop, so I don't need the speed. The older I get, the more I believe we don't need or want magnums. The less the velocity, the more the penetration. An exit wound means a blood trail, which in thick timber can mean the difference between killing an elk and harvesting an elk.