From Sierra:
https://www.sierrabullets.com/store/product.cfm/sn/2123/308-dia-135-gr-HPBT-MatchKing
With normal barrel twist rates for 308 and 30-06, this bullet will be spun too fast for best accuracy. But it'll still shoot 2" or better at 100'yards. The 30BR cartridge shoots 125-gr. bullets out at 3000 fps with 1:17 to 1:18 twist barrels producing best accuracy through 300 yards in benchrest matches shot for score. With the higher velocity these cartridges will shoot this 135 gr. bullet with the same peak pressure, that twist range will spin them at their optimum rpm rate. RPM formula: fps times 720, then divide by twist. Examples with max loads:
30BR with 125 gr. (3000 X 720) divided by 17 = 127,059 rpm.
30-06 with 135 gr. (3200 X 720) divided by 10 = 230,400 rpm.
308W with 135 gr. (3100 X 720) divided by 12 = 186,000 rpm.
I suggest reduced loads no more than 10% below max in listed data for these cartridges if best accuracy is your top objective. This will reduce bullet spin rate 10 to 20 percent. Anything less won't expand the case to chamber dimensions at peak pressure and will severely shorten case life with best safety. Excessive pressure ring stretching and expanding happens with reduced loads more than 10% below max charge weights in my experience. Reduced loads lower the spin rate which improves accuracy in these conditions.
308W with 135 gr. reduced 10% from max (2600 X 720) divided by 12 = 156,000 rpm.
All bullets spun too fast will jump too far from the bore axis from centrifugal force because most of them in a box of 100 are unbalanced a very tiny amount. Spun at the right rpm, they'll all shoot tiny groups.
