AA bolt design change

[dammitman]

so I just received and new hard use bolt from AA and it has the lug opposite the extractor and right on top the ejector with a machined out section. it leaves just a tiny piece on the back side that sure looks like a weak spot. anyone notice these design differences?

[D.Davis]

Yes, I got some like that. I call Alex. Arms about it they say it is a relief cut. It looks like it might be weak under recoil. ??? I like to lap the lugs to the extension, I am unsure about their new design. Dave.

[dammitman]

it sure seems obvious that the little piece is not going to hold any pressure at all so if it breaks like the first one did, ( I received a replacement when the first one broke the little piece off) should it not matter? should I run the bolt even with the little piece off? are we the only 2 who has seen these bolts? should I get some more turkey and sweet potatoes? all good questions,,,,,

[VASCAR2]

http://www.65grendel.com/forum/showthread.php?11817-Worth-paying-extra-for-AA-6-5-Grendel-hard-use-bolt

[ty_hooper12]

[dammitman]

i just don't understand the "relief cut" is my only question. that lug is now completely useless and might just as well not be there. i am sure they know what they are doing and bolts only really need the 6 full lugs to be right. if they will replace them when the little tiny piece breaks off i guess that's what they expect to happen.

[cb4017]

As I recall M-16 bolts have the same cut. I read about this years ago. Since there is no lug at the extractor, the lug opposite is relieved to avoid uneven stress on the bolt.

[LRRPF52]

The relief cut in the lug opposite the extractor is still meant to bear load, but balances the load of the 6 lugs symmetrically.

I think LMT used to do this on one of their enhanced bolts.

ArmaLite Inc. did it on AR15 and AR10 bolts where the rear of the opposite lug was relieved so that it bore no load.

Military bolts are not like this at all.

[zcostilla]

http://demigodllc.com/articles/the-a...nfantry-rifle/

Like any machine, the AR-15 has some parts that will eventually wear out. The bolt is one of these, contributing to both infant mortality failures and long-term failures for bolts with over 10,000 rounds. These failures usually involve cracks developing at the base of the two lugs adjacent to the extractor or at the cam pin hole causing the bolt to eventually break.

The AR-15 bolt can be thought of as starting with eight lugs around its circumference. One is cut away to provide room for the extractor. During firing, this asymmetry causes the bolt to warp slightly due to uneven support and put approximately 80% of the force load on the two lugs adjacent to the extractor. It's no surprise that the majority of bolt lug failures occur at one of these two lugs.

ArmaLite's solution is to balance the force by only using six of the seven lugs for load-bearing, restoring symmetry under load. This change is accomplished by simply shortening the back of the lug opposite the extractor so it does not engage the barrel extension. ArmaLite's engineering study determined that this change alone reduces the stress on the two problem lugs by about 40%.

[VASCAR2]

Good find Zac!