You peaked my interest on what was legal for elk in Arkansas. I looked through the regulations and it said that you can use a muzzleloader legal for deer. The regulations for deer is .40 cal or larger with a rifle. That seems like a great way to shoot an elk and never find it to me.
I’ve seen people have some very well placed shots with unmentionables in much more powerful calling bees and not find an elk. Elk are some of the toughest creatures on the planet. No way would I use anything less than a .50
I'm deciding on a caliber for my Kibler too. Think it's going to be a 58. I killed my first bear 46 years ago with a 45 cal, and several deer after that. Since then I've come to the opinion that bigger is better, especially when bear are involved.