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Old March 29, 2009, 07:21 PM   #12
Bart B.
Senior Member
 
Join Date: February 15, 2009
Posts: 5,467
I too, learned that Sierra retested all their loads; no significant changes. Thanks to powder companies sustaining their same formulas pretty good.

Years ago, I shot many matches with Sierra's head ballistics/testing guy, Martin J. Hull, who was a friend of mine for many years. He had loaded virtually all their test loads and shot 'em in all sorts of rifles as well as test barrels with many powders measuring their bullets' accuracy and developing loading data. He told me more than once that he never got as good of accuracy with any ball powder compared to the best extruded powder for any bottle neck rifle case. His best accuracy in test as well as rifle .308 Win. barrels happened with IMR powders. 4895 was best with bullets less than 160 grains, 4064 best with 160 through 190 grains and 4350 for 200 up through 250 grains. That's what all the best scores in high power matches were shot with when the .308 Win. was "the" cartridge to use.

Back in 1991 when a few of us developed loads for Sierra's new 155-gr. Palma bullet for its first use in international competition, the popular ball powders for the .308 were tested as well as extruded ones. A box of ammo using AA2520 powder was sent to an ammo test lab for pressure and velocity evaluation. We'd already done the accuracy tests. That load had the lowest spread in metered charge weight, peak pressure and muzzle velocity. Excellent data indeed! But it had about the worst accuacy. We ended up using IMR4895 with more spread in charge weight, peak pressure and muzzle velocity. Pressure tests showed a larger spike at its start with AA2520 compared to 4895. Convinced us that the bullet was being slammed into the rifling harder with AA2520 than 4895 did. We believed that's what deformed the bullets too much for good accuracy. Other handloaders using Oehler's peizioelectric pressure gages have also found out ball powders have a harder initial push to the bullet than extruded powders.
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