Lots of good answers so far.
Most factory percussion side hammer "traditional" ML's use a 1:48 twist. That is consdered a compromise twist, so that the buyer can shoot conicals and round balls. The 1:48 does neither extremely well, but is good enough to shoot both conicals and balls.
Your modern inline has a fast twist designed specifically for bullets vs patched balls and for higher charges. Usually 1:20 something to low 30's.
Nick is one the money with powder charges. For example, I have a .54 TC Renegade and a .58 custom flintlock. The .54 Renegade has a 1:48 twist, the .58 custom has a 1:66. The custom .58 has a custom Rice barrel with deep groves made specifically for patched round balls.
In the 1:48 twist, I shoot 90-100 grs of 2F, but in my slower twist 1:66 with the deep groves, I shoot 70-80gr's of 2F.
You CAN shoot the round balls out of your inline. But other than hearing the gun go off, why? They may likely not shoot very accurately. And, for hunting, the main mystique with shooting a hammer "traditional" type ML is a feeling of the connection with the past and, if a custom rifle, the incredible beauty of the woods and "the furniture", which is like the scrolled butt plates, trigger guards, etc.. That and irons sights and using a patched ball.
It isn't because the round ball is the most effective. A round ball comes nowhere close in killing power that the modern inline offers with jacketed bullets and high powder charges.
Here's some good info from TC. Scroll down about 3/4's tp find ballistics.
http://www.tcarms.com/assets/manuals/current/Shooting_TC_Side_Lock_Black_Powder_Guns.pdf
If I was using a modern inline, for hunting I'd use the bullets that match up best with your rig. And that's not round balls. If you just want to target practice and raise some smoke, then shoot up those balls, but at a target not gamr.
If you want to hunt with a roundball, then get a rifle that's best for it so no animals are wounded.
If anyone is interested in a custom Michigan made ML, go here. I own two of Ray Franks rifles. I just picked up a youth .32 for my girls to shoot target practice with daddy.

Ray has a great .62 flintlock he's making right now. It's got a very high grade curly maple #4 fullstock with silver/pewter furniture. He calls it "the bone cracker". I'd love to own this rifle and suggest it to anyone who thinks they want a great big bore flintlock. Wouldn't you love to thump a deer with that .62 ball?

Here's the rifle in the white...
http://www.sittingfoxmuzzleloaders.com/Early Pennsylvania Transitional Rifle.htm
Here's his finished rifles...
http://www.sittingfoxmuzzleloaders.com/finishedguns.htm