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Old July 15, 2013, 09:36 AM   #37
Bart B.
Senior Member
 
Join Date: February 15, 2009
Posts: 5,380
Phil, I wasn't making a comparison, just showing an example of how BC's can very with the bullet's speed through the air. The old 180 HPMK from Sierra held velocity better at long range and that's why the US Army Team had Sierra make them using the older dies after Sierra changed the boattail to that of the 168's. Those new 180 HPMK's would not hold supersonic velocity past 800 to 900 yards; just like the 168's. Extra tight barrels would shoot them fast enough to do so as their muzzle velocity was higher.

Having worn out a few 7.62 NATO Garand barrels, I've not noticed any significant degradation of accuracy as the throat eroded away after 3000 rounds and using M118 Match ammo with their bullets all seated to the same OAL. The several hundredths inch increase in bullet jump over that many rounds didn't effect any noticable accuracy change. The barrels still held at least 3/4 MOA accuracy at 600 yards from brand new to 2/3rds worn out. But the last 1000 rounds of the 5000 round barrel life did show accuracy had gone to about 1 MOA at 600. Which is why the Match Conditioning Unit rebarreled them at 5000 rounds. The bore erosion gauge read "5" at that point. Normal service rifle barrels were replaced when the gauge read "10" at about 10,000 rounds.
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