Thanks for the reply.I've never used anything over a 210 and that was a 338-06.I 'm not really sure what bullets to use.I've never had that much horsepower.lolI figured a 210 baenes or scirocco would do all I wanted to do.

In that case use the 1:12 twist. Out of curiosity, why cripple your gun with light bullets? In my eye the only credible bullet weights for the .338 bore are from 250-300 grains, this especially true for the UM.

I am havivg a 338 ultra mag built on a Ruger 1 action with a28 in. bbl.Pac-Nor is doing the work.My question is should I go with a 1-10 or 1-12 twist.I don't intend to use this rifle with bullets heavier than 210 gr.Its primary use is open country deer and elk.No dangerous game.I've used the Greenhill formula for twist rates and it comes out to 1-12 or slower,but the bullet mfrs. I've talked to say 1-10 for use wiht heavy bullets.I've measured the 210 scirocco,and even as long as it is,it will work with a 1-12 twist.Any info will be appreciated.