Sierra's 30 caliber 168 HPMK's proved dismal for long range accuracy (past 600 yards) from a .308 Win. case. That's why the US Army asked Sierra to make a 175 with a longer boattail so it would remain supersonic at 1000 yards from the 7.62 NATO case. The M852 round's original Sierra 168 was nororious for going subsonic at around 800 yards in 22 and 24 inch barrels as well as well worn 26 inch ones.
With 22 to 26 inch barrels in .308 Win., bullets having the best long range accuracy record are the 175's through 200 grain weights. 240's and 250's have been used, but only with longer leades so the bullet wouldn't seat too deep in the case. Bullets lighter than 170 grains need at least a 28 inch barrel and 155's have to leave at 2950 fps or more so 30 inch ones are the norm for use at 1000 yards. That was proved back in 1991 when the 155's were first used in long range competition and performed dismally in barrels less than 28 inches at 6600 feet elevation.
And no powder's equalled IMR4064 for bullets 175 to 190 grains or IMR4350 for 200's in the .308 case as far as accuracy's concerned. Varget's great for lighter ones such as 155's, but not these heavies. There's one or two Norma powders at the same speed as IMR4064 that'll give it a run for the money.
For best accuracy, you can slug your barrel's bore, measure its groove diameter then find bullets a few ten thousandths larger. Too bad Lapua no longer makes their excellent 185-gr. FMJRB match bullet at .3092" (7.85mm) that shot so well in factory oversize 30 caliber barrels.
US Navy Distinguished Marksman Badge 153
Former USA Palma Team Member
NRA High Power Master & Long Range High Master
NRA Smallbore Prone Master
Last edited by Bart B.; February 8, 2013 at 07:44 AM.