Bolt broke in my AR, ideas?

[QuakertownRich]

I didn't want to hijack the other thread, so started a new one. Little history before the break.
I bought the AR from my lgs about 8 mos ago, assembled from different origins as I didn't like some of the other complete AR's from factory. When I bought it, I also bought 1k rnds of Prvi Partisan 5.56 55gr BT ammo..the same ammo I broke the bolt with.
Components are L.A.R. Grizzly Lower, DPMS upper with 16" chrome-moly barrel marked M16 1/9. I only have about 800rnds through so far. Lately, it has been having some FTE's and FTL's. The other day it was horrible. Every other round was doing it, then this:



One thing I did do a little different than usual is, after the last time I shot it since I had only fired 60rnds through, I didn't clean it. I was having FTE's and FTL's occasionally before this though. My lgs stated there were layers of color with shiniest on the edge(believing this to be the final break) and that it probably had always had a crack inside, but didn't fail all at once. What say you?

[40twist]

WOW that SUX!!! Hey what does the cam pin look like?

[QuakertownRich]

I dunno, but prolly not good. After it happened, I took it to my lgs and he unjammed the piece of bolt, gave me back the bullet in the chamber, then replaced the bolt and cam pin. He only gave me the bolt the other day. I am to take it out and shoot it to see if any problems with FTE or FTL that would indicate any scoring occured elsewhere. I cleaned thorougly and lightly oiled in all the right places.

[imashooter2]

Looks like a factory defect to me. Any NDI should have caught the crack that started this.

[normanvin]

Looks like it has been cracked for some time.

[Guns4Fun]

Rich, i assume you must be the guy Dave Donley was telling me about yesterday when i was in his shop. Dave was telling me he thought it was cracked at the factory when they drilled the hole and somehow it got through their QC. Dave's been around the block a few times with ar's and for him to have never seen that before makes me think it is very uncommon. Did you get the bolt with the DPMS upper you used on it? or was it someone elses bolt?

I guess stuff happens sometimes. Good thing you were just target shooting when it happened and didn't get hurt in any way. Have you had a chance to shoot it with the new bolt?

[hower610]

You may find some answers here as well.

http://www.xdtalk.com/forums/ar-talk...er-survey.html

[DPB]

This does happen, although rarely.

Non destructive testing would not necessarily have shown anything. I have seen this happen to a military Colt M4 bolt. The non destructive testing of those is fairly well documented.

I suspect that most of your problems were due to the initial stages of flexing, and that the new bolt should fix the problem.

[Legion_Prime]

Yeah, you can see how one side of the break is all carboned up. That means it's been broken there long enough for the carbon to have buit up in there. I don't want to speculate as to when it would have initially cracked but this is the sort of thing the HPT and MPI tests are designed to make sure don't leave the factory. I'd say a new bolt and you should be GTG. Thanks for the pics!

[synergy]

A loose cam pin and serious over pressure could accelerate that happening, too.