I agree - although the guy who invented them, Mike ?????is a really nice guy.
Round balls kill all big game more quickly, within proper range, than does any slug from a muzzleloading rifle. One merely uses a bore size appropriate to the game being hunted.

I also agree on the big bore, while I have friends who've taken moose and elk with .50's I'd prefer something .54 or larger.

My own big game hunting rifles start at .58, then .62, then .69(14 bore). I personally prefer the 14 bore as a hunting rifle for moose and elk. It's .684", 482gr. ball makes an impression on the animals that is unmistakable to the eye, whereas the smaller balls or bullets make the animal take off in a mad dash as if only firghtened. I've seent his time and again with moose and .54's. I've not shot anything yet with either the .58 nor .62, so cannot coment on their 'impact' effectiveness. Only one moose ever walked off after being struck with a 14 bore ball, and that one shook end to end at the impact, then slowly struggled along for 20 yards, then collapsed.

I do not condone wimp charges for round balls on big game, nor do I condone big charges with slugs. The pressure difference is incredible. A large bore round ball, such as my 14 bore shoots, or a 12 bore Pedersoli for instance, will rarely generate over 10,00PSI with 150gr. of 2F GOEX powder, whereas a .50 cal rifle shooting a slug with the saem charge is pushing 30,000PSI. There are no barrels being made for muzzleloaders that I am aware of, made from 4140 chromemoly steel. They are made from softer materials, even 12L14, a leaded steel. GM barrels are stronger than that, but still not made from 4140. Heavy powder charges and slugs are dangerous - please don't use them. I don't care what the mfgr's and shooters of inlines say - round balls kill better than slugs on our game. We don't need something that works at over 200 yards - try hunting and getting closer. All my muzzleloading moose have been inside 95 yards & only one of those shot with a modern rifle was 200 - all the rest were inside 100 yards.

Ed Rayle will make any bore size and twist you want in a barrel.
Google Lt. James Forsyth's book, 'The Sporting Rifle and it's Projectiles". Either download it or I think you might be able to buy it somewhere. It's excellent reading and was the reason I had the 14 bore built back in '86.
If doing the same today, I'd probably have one made in 16 bore, to shoot a 1oz. ball, which shoots well with a mere 140gr. 2f. The point blank trajectory of these big bore rifles is 115 yards, where the ball is neither 2" above nor below the line of sight. They also have the power and accuracy for killing big game to 200 yards, if need be.

The last bench group I shot at 200 yards with the 14 bore was last July put 6 consectutive shots into a group 1 1/2" wide by 3 1/2" high. - open Express-type sights with a bead front. I was gong to fire 4 more, but decided 6 was enough to prove the rifle - and I didn't want to destroy the group - which I lost - of course.

A top of the back hold on a deer at 150 yards, is a deer shot through the middle, dropping on the spot or a short, huge blood trail.