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9/23/2020 3:47:02 PM
Posted: 12/28/2006 8:38:19 PM EDT
I read somewhere I think from Armalite the 6.8spc Bolt cannot handle the cartridge and causes bolt breakage. Is there any truth to this?
Link Posted: 12/29/2006 8:49:38 AM EDT

Originally Posted By farmboy292:
I read somewhere I think from Armalite the 6.8spc Bolt cannot handle the cartridge and causes bolt breakage. Is there any truth to this?



 Yes & NO & maybe. The first few rifles assembled used a 5.56 bolt opened up to the larger 6.8 casehead. This cuts through the outer hardened skim of metal & creates a weak bolt. Nowadays the boltfaces are machined before heattreat (hopefully) & this shouldn't be as much of a problem. Having said that, the bolts are still essentially 5.56 bolts opened up & are weaker than a 5.56 bolt. There is also the matter of some chambers & ammo being incompatable & raising pressure, thus contributing to bolt failure. Bottom line IMO, if you are using a correctly machined & treated bolt & ammo & chambers that are compatable, it should be fine, but there isn't much in the way of an extra margin of strength in these bolts. M9
Link Posted: 12/29/2006 6:31:29 PM EDT
We've shot a fair amount of 6.8 mm and have not seen any broken bolts in any of our weapons.
Link Posted: 12/30/2006 10:09:29 AM EDT
What about broken extractors?
Link Posted: 1/1/2007 3:46:47 PM EDT
[Last Edit: 1/1/2007 3:56:28 PM EDT by M9Powell]

Originally Posted By DocGKR:
We've shot a fair amount of 6.8 mm and have not seen any broken bolts in any of our weapons.



 OK, whats a "fair" amount & what pressure level was it loaded too? What kind of bolt is in it? To really answer this question it needs to have about 5 70,000 PSI proof loads fired in it & then be magnafluxed. Then 10,000 rds of 55,000 PSI loads fired in it. Now, when we have several thousand rifles that have done so, we can be confident in the bolts. Untill then we just have too make SWAGs based on the available evidence too date. My guess is its borderline acceptable. Some 5.56 bolts fail when subjected too the above treatment. This bolt is a weakened 5.56 bolt. I would expect more of them too fail than 5.56 bolts. An AR has its strong & weak points. The bolt is not a strong point of this design. It was originally designed for the triple duece. I'm quite sure its plenty strong enough for the 222. Then we crammed the slightly longer & higher pressure 5.56 into it & it still lives good enough. Then we crammed the 7.62X39 & PPC cartridges into it & started having problems. The boltface on a 6.8 is between 5.56 & 7.62X39. I'm sure it'll live at a certain pressure & for a certain service life. I just don't know what either of those points are & at this time I don't think anybody else does either. M9
Link Posted: 1/2/2007 4:06:33 PM EDT
Has anyone encountered an unusual amount of broken extractors?
Link Posted: 1/2/2007 9:34:45 PM EDT
Link Posted: 1/3/2007 7:10:34 AM EDT

Originally Posted By AR15barrels:
Is 5 rounds of HPT the official testing procedure?
I had heard it was one round per gun before testing.



 I'm not sure what the manufacturers requirements are. Thats my unofficial test for a match rifle that is going to be firing near proof level loads as a regular diet, fired tied down to a duece & a 1/2 tire remotley from cover. M9
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