Re: 338 edge barrel length
You can go with 1:9.3 to 1:10 twist. Broz is right give us a little more information on what you plan using this rifle for and we can better help you. You are going to lose 15-25 fps per inch depending on the individual barrel.
" Long distance shooting is an art, often meaning something you have mastered through innate aptitude or long range practice versus a simple application of science" .................Jeff Hoffman