Anyone witness or experince a broken or cracked AR bolt or carrier?

Me personnely:

1 short stroking AR. Gas key was loose on the BCG.

1 jammed AR. Locking lug next to extractor had broken off, jamming the rifle.

BSW

Seen three broken bolts. I forget the details now it has been so long; but it was posted here if you feel like searching.

Seen one brand new bolt in a brand new barrel that failed to headspace. Never did find out what the problem was though.

Seen several loose gas keys on bolt carriers; but other than that haven't seen any issues.

I have seen a few broken bolts as a small arms repairman.
I have seen commercial bolts that have peened out the lugs.
If you aren't counting your rounds fired by cases of one thousand instead of by the individual rounds, I wouldn't get too concerned.
Mil-Spec bolts are made from Carpenter 58 steel and this stuff is fairly soft, even when heat treated.
Thios steel can have small imperfection cracks and still function for thousands and thousands of rounds before it fails as long as it has been heat treated properly.
Magnaflux Particle inspected bolts fail too.
Like I said, the only bolt failures I have seen were in service and all those bolts are supposed to be M.P.I.ed.

I haven't witnessed a bolt fail in action, but I saw a cracked one a day after it happened. I don't know detailed specifics, except that most (perhaps all) of the guns being shot were full auto Colts, and since they were academy guns (and based on the number of rounds our class alone fired) I'm guessing the guns had some pretty high round counts.

ETA: The instructors were all sort of fascinated with the bolt, so I got the impression they didn't see that sort of thing very often.

One of our juniors had either a loose key or one that sheered off at Camp Perry last year.

I've seen plenty of broken bolts, but understand our situation is well outside the norm for most folks.

One of the shooters in our group is a lifelong bachelor nearing 60+ years of age, who has been shooting AR's and M16's since the 1960's. Somewhere in my vast collection o'crap I have a shoebox full of broken parts from his various guns, including 5 or 6 broken AR bolts. The remainder of parts are from AK's, SKS's, Garands, etc...

At least 5 AR 15 bolts broke in half at the cam pin hole. The other one I can recall broke near the extractor. The volume of ammunition he has shot in his lifetime is difficult to pinpoint, but a conservative estimate would be well in excess of 1 million rounds of center fire ammunition, not all of it in 5.56. He held a dealers license in the 70's and owned many Class 3 toys at the time. His surplus ammunition purchases tend to run in the 10's of thousands at a time, back when surplus ammo was selling between .05 and .10 cents per round.

But to answer your question, in normal use, I've never come across a broken bolt. But in the service of the above gentlemen, he has a habit of rarely cleaning weapons, and only changing parts when the weapon fails to function properly. Two of the broken bolts exhibit severe gas erosion on the bolt face surrounding the firing pin hole. This erosion is/was caused by worn and loose primer pockets from brass that had been reloaded many, many times. His favorite lubricant is 30w motor oil, which tends to make the weapon smoke profusely upon extended strings of fire, but also gathers the burnt powder, dust, and other debris into a fine compound that coats the interior and exterior of the weapon.

He was the first person I know to successfully use the 115 round AR-15 Chinese drum (downloaded to 90 rounds) on full auto and get reliable functioning. Somewhere on an old hard drive I have a .avi file if him ripping off a 90 round burst with his Phoenix Arms conversion. It was a sight to see all that smoke and fire.

He is also the only person I have seen to successfully destroy an AK by shooting it until it fell apart. He had an NHM 91 with a thumbhole stock that was fed over 75,000 rounds of cheap 7.62x39 until it was corroded and worn to the point where he could not hit a steel target at 100 yards that was 4' x 4' in size.

In normal use, I would not expect a bolt failure on an AR-15. Almost all of the parts he purchased as replacements/spares were from either M&A Parts, or Model 1. I know one of the broken bolts is of Colt mfg, the other is unmarked and appears to have voids in the metal, so I suspect a cheap(er) import part.

Ar's are tough. The only part I have to have in my kit is replacement extractors. YMMV.

I had a case head seperation/detonation about a month ago...
I believe the cause was a severe undercharge.

The carrier lost its underside supporting the bolt,
which had its extractor severely bent.
The bolt went back into service without problems.

The carrier was replaced with a Young NM lite carrier from Denny's.

Works like a dream.

I triple check my loads as well as all work.::banghead:

docgary