Greydog is of course right.
So why do I recommend 9 twist? A few years ago I had a "10 twist" Shilen chambered in 257 Roberts AI. With bullets up to the 100 B Tip in length, it would shoot 3/4 MOA at worst. Anything longer it opened up closer to 3 MOA. Bullets like a 100 TTSX or a Berger 115 VLD were a pipe dream in that barrel.
The cleaning rod told me that although spec'ed 10 it was more like 10 3/8". Since the extra twist doesn't hurt anything I hedge my bets. In fact some might argue faster twists blow up varmints better and are more decisive on larger game.
Then start shooting that in 20 below weather and see the wheels really fall off.
9 all the way
