I have had 243's and 6MM's in several twist rates. 1 in 12 worked just fine with bullets in the 75-90 gr. range, the 85 gr. Sierra BTHP being extremely accurate. In 1 in 10 twist rifles I had no problem stabilizing the 105 gr. Speer spitzer, a great bullet by the way. The several 1 in 9 twist rifles I have owned shot bullets of 75 grs to 105 grain bullets, everything I tried worked nicely.