1/10,1/11, or 1/12 twist will work. The long range shooters lean towards 1/11 and sometimes 1/10. These offer a chance to stabilize heavy 175gr and 180gr bullets. I shoot a 1/10 with 168's in my M1A service rifle but limit to 600 yards.
Beyond 600 yards the 308 needs stiff loads to remain supersonic. The 175 SMK was designed for this purpose and is very popular. One shooter likes the 30-06 for 1000yards with a 1/11 twist but with the '06 he can launch 190's and 200gr. slugs.
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