Sheared bolt lugs

[everyreggie]

Hi all,
I was hoping to get some help with this....the other day i was at the range and sheared the lug on each side of the extractor off my bolt.
Doesn't look as if there is any more damage to the barrel ext. or anything else.
I think it may be the O.A.L, I am running Hornady brass with 123 A-max at 2.260...I think it may need to be more like 2.245 but was unsure if this was even the reason?
Any ideas?? I can add a pic of bolt if that helps!

Thanks in advance!!

[everyreggie]

Just realized there is a troubleshooting area...please feel free to move if needed!!! Sorry !

[infidel470]

Please provide more info: reload or factory ammo, how many rounds, any sign of hot load on the case, who made the bolt etc.
The reason behind the request is that many people on this forum have similar problems, some due to bad heat treatment on the some bolts, some due to hot reloads, some due to inproperly installed barrel extension

[everyreggie]

Ok here is the info:
-Les Baer Precision Bolt

-I have run approx: 900 rounds in past 10 months

-Reloaded ammo: Hornady brass, 123 gr. Hornady A-max, 30.2 Gr. of AA2520, CCI 450 primer. C.O.A.L of 1.526, O.A.L of 2.260

Thanks!!

[infidel470]

You load seems to be on par/or lower than the the pressure limits of the AR system in my opinion, but i `m not familiar with Les Baer chamber/ barrel dimensions. Have you contacted the vendor?
AA were excellent with the customer support in similar situations. If you contact Les Baer most likely the will examine the bolt and extension for overpressure signs and advise you of a situation.

[RedFalconBill]

That is a near max load with the Sierra and Lapua bullets. Have not used the Hornady bullets and quite frankly, I've gone to using the 100gr to 108gr bullets for most of my Grendel shooting.

Les Baer is a good company and if you explain what happened they can assist you.

Lastly, when a bolt goes, the locking lugs on either side of the extractor are usually the ones that shear.

[LRS_Ranger]

You might send Noone on here a PM.. he had an issue with one of his grendles in which he was told that the parts not being trued up caused uneven stress. He can explain it a lot better than I can, I isn't really smart..

[madcratebuilder]

You might send Noone on here a PM.. he had an issue with one of his grendles in which he was told that the parts not being trued up caused uneven stress. He can explain it a lot better than I can, I isn't really smart..

I've read about this and bought a receiver lapping tool. In my case the face of the receiver was not perfect, I figure I removed about .002-.003 of material on half the face to true it with the bolt centerline. I don't know if it helps, but it can't hurt.

[noone]

Yep, that was me with the bolt lug sheared just above the extractor. It was in a rifle I built myself using what was supposed to be a really "top of the line" bolt. After the first bolt sheared, I bought another one, thinking it must be my fault. Bolt #2 also broke in the same place. So I called ARprecision for some help.

I spoke with the gunsmith there (sorry, can't remember his name) and he told me that if the face of the upper receiver isn't truly square with where it mates up with the barrel extension shoulder, when you torque the barrel into the upper, you actually end up pushing on one side or the other of the barrel extension more than the other. This uneven pressure causes uneven pressure on the bolt lugs. Here is where this story gets really good.

ARprecision wanted to figure out what was causing the breakage so they could build better rifles for other people. Keep in mind that they didn't build the rifle for me..I built it. The gunsmith there said that about 75% of the "normal" upper receivers don't have really true facing where the upper receiver and the barrel extension mate up. With AR15's, there is more material around the bolt lugs, so the problem isn't quite as noticeable.

They asked me to return the rifle, broken bolt, to them to look at. I paid for a new bolt, and they trued up the upper receiver face, checked out everything to insure that everything was square, and in spec as it should be. With the new bolt installed in the squared up receiver, I have put plenty of rounds through the rifle without a hitch. So I'm convinced in what they said as their fix worked. The really cool part is that all I had to pay for was the bolt..all the other work was done for free.

That is the second place involving the Grendel where I have received fabulous customer service. Alexander Arms was the other one. I got stung buying a rifle that was advertised as an Alexander Arms build. It turned out that the rifle was built using some Alexander Arms parts, but was not assembled by them. Bill Alexander had the entire upper rebuilt with a new Shilen barrel at a price that was truly wonderful. I guess he took pity on someone who really wanted one of his rifles, and just wanted another happy customer...he got one.

As Mr. Alexander explained: If I go to the range with a rifle that I think is an Alexander Arms rifle and it doesn't perform well, that isn't good. On the other hand, if I go to the range with an Alexander Arms rifle that performs well, and I am happy with it...that is a kind of advertising that is very hard to get. The rifle Mr. Alexander built for me won the very next precision rifle match I used it in. So, I guess he got the advertising as lots of people were asking me about the rifle. It obviously performed very well indeed.

[pappy42]

I've read about this and bought a receiver lapping tool. In my case the face of the receiver was not perfect, I figure I removed about .002-.003 of material on half the face to true it with the bolt centerline. I don't know if it helps, but it can't hurt.

Which tool did you get? How hard is it to use? Thx

[madcratebuilder]

Which tool did you get? How hard is it to use? Thx

http://www.midwayusa.com/viewproduct/?productnumber=810457

Midway and Brownells both offer this tool.

My tool had been dropped during shipping and had a ding right on the edge that deformed some metal. A little hand work and it has fine. The tool can be a very tight fit on some uppers, you may need to take some 600-1000 grit to the body of the tool and spin it to remove any burrs or machining marks so it well fit through the barrel extension hole on the upper.

The pilot shaft that the drill chuck attaches to is a little short but should not be a problem with a quality chuck.

I used some fine grit valve lapping compound I had on hand and I only took 20-30 seconds total with the drill the face the upper. Run the drill for a few seconds and check, do this until it has faced the entire face of the upper.

[noone]

The ones I have seen at Brownell's are not too expensive, and are really, REALLY easy to use. Insert where the bolt carrier goes, twist them a few times..just like deburring a case neck.

[cornholio1]

Bill Alexander really stand behinds his products. He will answer the phone personally. I had sent him my upper once to verify a chamber issue. Well, there was no issue, but he did say I built a decent rifle and made suggestions in improvements suck as a steel vs aluminum gas block etc.

He has seen a bunch of wahoos who don't know how to build a rifle send junk to his company. Some install the gas tube backwards, loose handguards etc. I hope my Grendel comes back soon

[Bill Alexander]

Obviously I cannot verify which upper this is from the screen name but it should be on the way back. Please call Melissa on Monday for tracking info.

Misalignment of the planes of locking lugs on the barrel and the bolt will create stresses which will accelerate failure. The front face of the reciever can cause this probem. Loose fitting barrel extension to reciever joints allow movement in angular and axial planes which is always a problem, if only with accuracy. Barrel extensions should be checked for thread to locking face alignment and most importantly should only be installed once. Removal of the barrel extension and reinstalling will often shift how they mate. Military tightening specifications will plastically deform the barrel threads and shoulder and must not be used for best builds.

One of the goals of the enhanced bolt system we make is to reduce the sensitivity to alignment. We are currently in a slight redesign to improve the stress raisers at the extractor cut and the durability of the spring. The heat treatment is being examined to see if newer methods can yield a more effective overall design.

Bill Alexander

[ss355]

Armalite relieves a few thou from the bearing surface of the lug opposite the extractor to better balance the load on the six remaining lugs that do bear load. There's an article on their website that explains this in greater detail. I can't help but wonder if this lug-relieving procedure would help in an instance like the original poster mentioned. Thoughts, anyone?