5R, the reason Sierra developed their 30 caliber 175-gr. HPMK was Lake City ammo plant asked them to 'cause the Sierra 168 HPMK often went subsonic before getting to 1000 yards. Such is life with M852 ammo shot in M14's 22 inch barrels. So, 'twas only business sense to sell the 175's at retail.
Their BC's almost exactly the same as the old 172-gr. FMJBT match bullet that was designed in the mid 1920's after tests with them at the seashore in Daytona Beach, FL. That bullet in M118 match ammo easily stayed supersonic through 1000 yards in 22 inch barrels.
Dan, I think handloads would have had a longer accuracy life in that barrel. Even if they used the same load but kept seatting the bullet out to contact the lands, that would reduce the bullet's tendancy to enter the rifling crooked when it had further to jump from seated position. But probably not more than 10% longer barrel life.
.2 to .3 inch average at 100 yards is about the best one can get with the rifle shoulder fired. Even with a rifle that shoots .1 inch from a machine rest. Us humans are not all that repeatable holding a .308 Win. rifle into our shoulder and having it recoil exactly the same for each shot. My guess is if the rifle had been fired from a machine rest, the groups would be .1 inch smaller on the average. And they would also probably be more linear from small to large; that's how the bore erodes.
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Former US Navy & Palma Rifle Team Member
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Last edited by Bart B.; March 2, 2013 at 12:05 PM.