A minie-ball-type .58 cal (24bore) 560gr. Hollow Base projectile will shoot well in as slow as 78" - witness the 3 band Enfield having 39" bl. Local chap (Vancouver Island) made 4 hits out of 10 shots, on a 6' steel plate at 750yards, offhand, with just such a rifle and bullet. He placed 2nd shooting against Sharps, Remington, Ballard and Winchester ctg. buffalo rifles.

This 78" twist was later changed to 48" in the shorter 32" 1858 rifle bl. and 24" bl. of the carbine of 1861.

We know, that for an elongated projectile to shoot well, the smaller the bore, the faster must be the twist.

A 12 bore, even meant for slugs, can utilize much slower twists than commonly thought. Do we actually need the overstability of faster twist rates?

When the rush of rifled 12 bore barrels hit the market in the 70's and 80's, I was quite astounded at the seemingly fast rifling twists.

I do think it is an error to adhere to the mid 1800's English gun maker's penchant for super fast twists in the large bores, especially if one is thinking of shooting round balls as well.

A standard 7 dram heavy 12 bore load for the 2 1/2", 2 3/4" or 3" case, should produce about 1,550fps with a round ball.

Weighing in at well over 1 1/4 ounces, a .730" ball or larger, is a lot of power for the Martini - with any of the normal 12 bore black powder loads. Smokeless lends even more power & less felt recoil as well.

In a muzzleloading 12 bore, if using a .715" ball, in pure lead, about 545gr. - driven to 1,350fps by about 120gr. 2F, is lots for most NA game.

A .710" ball will run about 536gr. range.

In the late 1868 & later era, the Sharps and Remington RB's in .50/70 were rifled one turn in 42". My .50/70 Carbine shot very well to 450yards with 450gr. bullets, an inch long, too long according to Greenwell's twist chart - but they shot well, 4 out of 5 rams at 450yards, with 20" bl. carbine.

The later .50/90 buffalo Sharps(as well as those lengthened to 3 1/4" case on the frontier) were rifled one turn in 36".

That twist stabilized bullets quite well to about 600gr.

I always thought 36" was faster than needed for a 12 bore rifle shooting bullets to 600gr. or 700gr., and still do.

As well, my Uberti Winchester model 1876 in .50/95, shooting short bullets (7/8") to 450gr. at 100 meters, 2 1/2" with open sights, has a 48" twist.

I got to the buffalo at our Black Water Range, 1,000 meters using a Lyman mould in 368gr. with the rifle's ladder rear sight from Smith Engineering in Oregon, along with the factory blade front sight. Do you need 36" for a 12 bore - I don't think so.

I would ask Bobby what he thinks on this, Tom.