Another is Ed Rayle. Could find his number if needed. Same with Bobby Hoyt.

I would suggest a twist of no more than 70" or 80" at the most for 12 bore. The same can be said for 8 bore.

My .69, which is 14 bore, had non-diminished accuracy from 125gr.2F through to 200gr.2F. It has a 66" twist.

My buddy's .75 (11 bore) also shoots well with 200gr. and it's only a 60" or so - might be the Getz standard at 56".

You might find you do not like shooting something that requires more powders than these rifles.

Keith's rifle also does fairly well with 125gr.2F and with a 600gr. ball, that's actually quite enough for us. With that charge, it actually keeps a hardened ball inside a moose.

More than that and they exit.

My bro shot a moose many years ago with a .75 Brown Bess, using a pure lead .735" ball with 100gr. 2F. I have the ball in my 'stuff' here somewhere and it measures 1 1/4" in diameter, only about 1/4" thick and stopped up against the hide on the offside, ribs penned both sides, with a 2 1/2" hole through the lungs.

I also suggest no more than .012" depth of rifling.

Perhaps .005" depth and a 102" twist would be fun to play with - or not.
It would take a looser load, that is for sure. Heavy charges and deep rifling in 60" to 66" takes a very tight ball and patch combination.

Some sort of wad between the patched ball and powder will allow a slighlty looser combination as well.