Way back in the dark ages I saw a simple formula for determining twist rate based on bullet diameter and I think bearing length. It seems to me it was sorted out and simplied by Homer Powley or one of those early gurus. I can't seem to find it, does this ring a bell with anybody?
I didn't know if this was a gunsmith or wildcat question, but you never know how deep the water is until you jump in.
Thanks
Bfly

It is called the Greenhill formula.

You won't find a better site than this one.

http://www.riflebarrels.com/articles/bullets_ballistics.htm

Ray