I though he was talking about muzzle loader's. I don't know squat about them but read or saw at one time that in the muzzle loader days the most highly desired one was a 50 cal. Probably for the caliber of the bullet. Something I found in my 308 shooting cast bullet's, the heavier bullet's seem to shoot better and hit harder. I'm guessing in a muzzle loader a heavier bullet will also hit harder.
I am not much on modern muzzleloaders, having never even touched one, nor ever used Pyrodex or shot a bullet from one of my front stuffers. Along with never having played golf, or worn wingtip shoes, one of the things I take a modicum of pride in. That said...
I would not hunt elk with a .50 patched round ball. If I did, I would shoot a two-ball load. It seems, from my friends' experiences, that .54 is about the sweet spot for mass and velocity when it comes to hunting elk. I have a .62, but it flat gets painful to sight in with hunting loads and has a rainbow trajectory that the .54 outdoes. All of the above is patched round ball, not bullets. Heavens, I can't imagine the recoil from a hunting load in a .62 behind a bullet...
I am not versed in the ballistics of the newfangled rifles. I tend to think that they are oversold and overbragged a touch, but I'll not find out because I have other funner stuff to shoot. But if you are hunting with open sights, my money is on you being able to shoot effectively at about the same range with either the modern or traditional approach. It is possible to find very nice traditional rifles that would be ideal for elk hunting, at a decent price, both new and used. I like the satisfaction of shooting the old way, using balls I have cast and shot in a rifle that I built.
I am not trying to be preachy - just saying you can consider an alternative. But you can find new in-lines cheaper than traditional rifles, and they are by-golly accurate. Which ever brings you the fun you seek - you have lots of choices. And if they can be kilt with a bow and arrow....