Been working for a few hundred years, has killed every critter on earth, and still works well.
Again, at blackpowder velocities, nothing will possibly beat a chunk of solid lead, the heavier and closer to bore diameter, the better. Whether the projectile is round or bullet-shaped, solid lead and black powder are a match made in heaven. There is nothing better, even if there are things that are newer. Modern bullets are designed for high velocities and smokeless powder.
Been using powerbelt 295 and 3 777 pellets! Most deer �� shot haven't moved. Shot a 250 pound sow last year she made it about 50 yards. Used a Maxi ball years ago and they worked too but powerbelt easier to load if you need another shot!
Newer and fancier isn't always better. AT blackpowder velocities, absolutely nothing beats a solid chunk of lead. 350 grain T/C Maxi-hunters hit deer like the hammer of Thor. And yes, they work just fine in an inline. I finally go my inline shooting buddy to try them, and after shooting a few deer with them, he threw away all those half-plastic bullets. Just because you have a plastic gun doesn't mean you have to shoot plastic bullets out of it. Try it, I think you will be surprised, pleasantly.
I shoot the 45/70 Barnes Original 300 Gr with the orange sabot. But I shoot it in Savage ML with smokeless Vihtavuori N120. They shoot great. I know. It's not really like using a muzzle loader but you asked.