Bob, I like your idea about the 60" twist as opposed to the 35". Back in the hayday of double ML's for dangerous game, the English makers were hung up over using twists in the 36" range, as noted by Forsyth in his little book " The Sporting Rifle and it's Projectiles" printed in 1861 or 2.
; He noted the fast twists stripped balls, and recommended slower twists, as slow as 1 in 12 feet in some instances. We know today, that is too slow as enormous charges are needed to get stability in those rates of twist.
; 60" to 70" would probably handle quite well with round balls and short slugs. My own 14 bore (.69 cal.) rifle, with it's 66" twist shot amazingly well with RB's as well as slugs in the 600gr. weight. 5 shot round balls groups off the bench ran 1 1/2" consistantly, over a 20 years of such use with only the express sights for aiming. The heavier slugs greatly increased recoil and were not used much, only for testing, however they did shoot to the same sights to 50 yards and ran roughly 2" fo groups, much larger than round balls.
: The round balls, if slightly hardened, would exit a moose so more penetration wasn't needed. RB's in pure lead weighted 480gr. at .680" diameter, while WW balls at .683"(same mould) weighed 466gr. I ran the balls at 1,550fps, same as my 12 bore ctg. gun did with 5 1/2 drams (150gr.) of 2F and .715" balls at 545gr. in pure lead.
: For most hunting, I'd use RB's and pick a rate of twist expecially for them. The 60" to 75" would be IT. Comprimise twists, like the 35" normally avialable nowadays, interest me little as they usually fail to deliver the best results from either projectile. My 12 bore double gun would average 2" at 25 yards, shooting lefts and rights, and it was a smoothbore. Longer range shooting would be necessary for a rifled bore to show it's potential, I believe.
; I suggest picking the appropriate twist for the projectile you wish to shoot.