02-06-2012, 06:18 PM
bwaites Wrote: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!
thanks for the info, I had read quite a bit about failed bolts for 7.62x39, even in that cartridge....but the 7.62x39 bolt is a little less recessed than the standard Grendel bolt, correct?, which should with a deeper chamber and strong bolt allow greater pressures? Also, I think the superbolt that ARP makes will handle about anything thrown at it. I'm going to try their new barrel/bolt combo for my next Grendel build and see how their chamber and 5R rifling does for accuracy, looking for a hunting rig, don't mind carrying around my 24", but like the 18" size and I use mainly 16" in my 6.8's, two being 16" (well actually 3 as I have another coming in today, the Bison 16" BSP that i'm going to try subsonic) and one being 20"