02-06-2012, 05:42 PM
elkbow Wrote:oops, yep backwards, the less recess is on the 7.62 bolt, which should allow for higher pressures of the round, thanks for correcting that, not the first time i've brain farted on that
Not so much, actually. The Grendel bolt was specifically designed for maximum strength, and the steel was changed from the Carpenter 158 used for 7.62x39 bolts to a much stronger alloy. 7.62x39 bolts failed regularly, even at 7.62x39 pressures, and it was one of the issues associated with making it run in an AR. (Along with feeding issues because of mag incompatibility due to case taper.)
Alexander significantly upgraded the steel, and that, in combination with appropriate pressure levels, improved the bolt life. 7.62x39 bolts used by others in 6.5 builds have been less successful. Several years ago I kept a running tally of all the bolt failures and the causes, as well as where the bolts originated. EVERY AA bolt that failed, except one, failed in hand loaded situations. 7.62x39 bolts failed without any significant pattern. They failed with factory ammo, hand loads, or a combination. The one AA bolt that failed with factory loads failed with a steady, almost exclusive, diet of Les Baer 123 ammo. Since others shot that without issues, I never could come to any real conclusion on the cause. Maybe just a bad bolt. Les Baer's old Sierra 123 load was very warm in comparison to other factory loads, though!
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