As a general rule roundballs require a slow twist. M/l that are intended for slugs (elongated projectiles) have a faster twist. Some factory made rifles such as the once-very-popular Thompson Center "Hawken" had a middle of the road twist that would work okay for either short, fat slugs or patched roundballs. My rifles are all handmade and have 1 in 66" twist. The twist rate needed is also partially dependent upon the velocity.
I can safely shoot extremely heavy charges in my Leman Trade Rifle that I built in 1983, it being a .54 cal. with a 1 1/16" octagonal barrel (Green River Rifle Works barrel with 7 lands and grooves). I have shot up to 200+ grs. of Goex 2F with good accuracy, but normally used no more than 120 grs. for deer. When I competed with that rifle in NMLRA matches I used much lighter loads at 25, 50 and 100 yards ........... 50, 60 and 85 grs., respectively. Super accuracy across the board. In competition I shot home cast .537" balls with teflon coated, and slightly dampened, pillow ticking. I had to seat the ball in the muzzle with a mallet and a short starter, but the accuracy was phenomenal. I have a home=made .45 cal. "buffalo rifle" that I made for cross-sticks matches that has shot 5/8" five shot groups at 100 yards. I have the target to prove it. The accuracy potential of good roundball guns are grossly underestimated by the general shooting public.
The killing power of a roundball is hard to overstate. One Thanksgiving morning I was walking the squirrel woods with my Appalachian Po-Boy .36 cal. long rifle, looking for head shots on squirrels. It was loaded with a .350" ball, and pillow ticking patch. It was too windy for good hunting so I slipped along quietly into a new-to-me area of the woods alongside a big beaver pond. Suddenly a buck jumped up out of a grass thicket across the pond and began running laterally to me, left to right. I instinctively pulled the hammer to full cock, shouldered the rifle and swung ahead of the running buck. As I did so I quickly thought about how I had a very underpowered load for an adult deer, so I tried a head shot, leading it a couple feet at about 60 yards. At the shot the deer looked to be dropping its head to go through a hole in a big briar patch. I reloaded, eased across the beaver dam and found the buck dead on the other side in the briar patch, shot clear through the neck just a bit behind the head. I hadn't led it quite enough for a head shot, but got complete penetration of the neck with little .350 ball and a pipsqueak charge. I probably wouldn't try that again. Much luck involved there.
