I am having a 338 ultra mag built on a Ruger #1 with a 28 in. bbl. I am going to use 200-210 grain bullets.Everyone says I should use a 1-10 twist.I did the Greenhill formula to calculate the twist rate for the bullets I'm planning to use and it comes to 1-12 or a tad slower.I won't be using any bullets over 225 grs. max.I would appreciate some suggestions for those of you that use a 338 UM,particularly those of you that use lighter bullets. thanks.