TWO broken AR bolts in 500 rounds

[damon1272]

Hey Damon I don't feel like I'm being irresponsible here. I did a ton of research on what may be causing my problem, and the majority of the information I got lead me to believe that my bolts may be of low quality. Believing this, I went ahead and purchased a very high quality, highly rated replacement. That part lead me to another question. I'm using the forum, and the community at large, to get a wide range of possible views on my problem. I think that's what a community is for. I am sure there are some qualified gun smiths on here who could help me get to the bottom of this issue.

That being said, right when my second bolt broke, I brought the upper and the broken bolt into a gun smith, and he was stumped. That's why I'm here.

I'm not being irresponsible. I'm using everyone here to help me solve a problem.

Hey bud just don't want to see someone get hurt because of bad advice on this forum. The biggest thing you need to do is have the rifle headspaced before just throwing a new bolt in. Based off the low post count I figured you may be an inexperienced shooter (may not be a fact but just guessing).
Though my response was terse it does come from the point of saying please read some books, not just the internet for information. Reason being there are guys on this thread that post like they know what the heck they are talking about and have high post counts but in the end don't know squat. Other folks are giving solid advice.
Lots of info to be gained from books about metallurgy, gunsmithing, and reloading books that will really help your knowledge and ultimately lead to wisdom when playing with guns. The strength of the AR is in some respects its downfall. It is too easy to play with at most can plug and play and not know that they are getting into trouble or causing future problems.
Sorry if I came off as an jazz but it was more from others comments and seeing someone going down a path that could potentially get hurt.

[Sputnik]

[ar15barrels]

So the barrel extension should be harder than the bolt?

The general rule is that the bolt and whatever it locks into should be 10 points difference on the C scale.
It does not matter if the bolt is harder or receiver is harder, but usually the bolt is harder in a bolt action rifle.

You want the smaller/thinner part to be the harder one so it will be stronger.
In the case of an AR, the barrel extension is the harder part.

[Wrangler John]

Well, then there's these:

http://jprifles.com/1.4.7_Bolt.php

But headspace is important too, especially when having all that stuff flying around ahead of one's soft warm face. I'm paranoid about such things, it's like keeping the leg wires of electric blasting caps shunted during storage in a proper container. Buy a set of gauges, check often, what's to loose?

[Jimi Jah]

Brand/source, or is this a secret?

[nothingcoolatall]

The brand of the uppers was from Valor Industries, out of Apple Valley, CA. Obviously it's just a company that puts together component uppers, but everything else seems to be great quality. I've called them and they told me to send it all back. Maybe I will.

[russ69]

Interesting because if you look at any other thread ever of ar15.com or other comparable sites they all say no don't do it. Even the army says don't swap bolts once they've been mated with the barrel....

...Also, the habit of swapping bolt carrier groups back and forth between two barrels is a bad habit as it causes additional wear on the bolt...

...Reason being there are guys on this thread that post like they know what the heck they are talking about and have high post counts but in the end don't know squat...

Remember 20 guys can give an answer and it still can be the wrong answer. Engineering is not done by consensus. We may never know the complete story without a full engineering analysis but constantly swapping bolts is not helping the issue.

[God Bless America]

True. Didn't want to get into that as even MPI confuses most people here.

You are too kind.

[nothingcoolatall]

I gave Dean Wilkerson a call up in Van Nuys, and he says it is very very unlikely there is a headspace issue. He has only seen it twice in his life. He also said that sends the bolt has been replaced, checking the current headspace probably would not clue him in to whether or not there was a headspace issue before. He said it sounded like a total mystery. At this point I am guessing there was some manufacturing flaw with that batch of bolts. I'll put a couple thousand rounds through it with the new reliabolt and see how it performs.

[ar15barrels]

I gave Dean Wilkerson a call up in Van Nuys, and he says it is very very unlikely there is a headspace issue. He has only seen it twice in his life. He also said that sends the bolt has been replaced, checking the current headspace probably would not clue him in to whether or not there was a headspace issue before. He said it sounded like a total mystery. At this point I am guessing there was some manufacturing flaw with that batch of bolts. I'll put a couple thousand rounds through it with the new reliabolt and see how it performs.

Dean obviously does not see as many AR's as I do.

If you can't see the peening on your bolt lugs and understand that you had excessive headspace when the bolt failed, I don't know what else to tell you.
The cause of bolt breakage is bad heat treating.
The cause of the peening you have is also bad heat treating.
I have another bolt in my shop with similar peening to yours that shows about 0.030" of excessive headspace.

[nothingcoolatall]

That makes sense. Too much room for the bolt to slide back into the lugs before rotating and sliding out of battery? So you think the breakage is cause by bad heat treating, but regardless the headspace must have been excessive?

[ar15barrels]

That makes sense. Too much room for the bolt to slide back into the lugs before rotating and sliding out of battery? So you think the breakage is cause by bad heat treating, but regardless the headspace must have been excessive?

The headspace was excessive because of the lug peening.
The lug peening occurred because the bolt was too soft.
The bolt is too soft because of poor (or NO) heat treating.

If you brought me the bolt, I can poke it with the hardness tester and see how hard it is.
I bet it's around 20 when it should be in the 40's.

[nothingcoolatall]

Hey bud just don't want to see someone get hurt because of bad advice on this forum.

Totally get it. Thanks for looking out!