Well, I finally decided I'm going to order a custom .50 barrel for my Pro Hunter from SMI. I sold a few guns and was going to try to get started in bowhunting, but I don't think I would like shooting a bow as much as much as a gun. I was (and still am a little) hesitant to spend the money on a custom barrel, but finally just decided it's a one time thing and might as well do it and have fun with it.
So, I can order about whatever twist I want. I read where guys have gone with as fast as 1 in 22" to as slow as 1 in 32", which is the SMI standard twist. I plan to shoot 250 to 300 gr. primarily but I'm sure I'll shoot some lighter and some heavier. The 300 gr. SST's I have are exactly 1" and using the Greenhill formula I would actually want something close to 1 in 35" but that seems too slow. I was thinking 1 in 24" but really don't know.