AR-15 Critical Failure — Bolt Breaks into Two Pieces
A while back, our friend Dennis Santiago was conducting training for a Southern California Police Department. During a training session one of the unit’s AR15s stopped functioning. The problem — the bolt in the AR rifle broke in half. Dennis states: “They ran the gun dry, broke for lunch, shot it again. They don’t like that. I personally like to flood the bolt wet with lube on training days. It prevents stuff like this. Given that, it’s a simple remove-and-replace fix.”
Here are some of the more interesting comments about this parts failure — an AR bolt that literally sheared in half:
“If I was a betting man [the steel] wasn’t made by Carpenter Steel. They are one of the few companies that use the correct [milspec-steel, C-158] called out on the drawing which they coincidentally developed. Most of the other companies that make [AR Bolts] use different steel with the same heat treat specification as what is called out which gives them the potential of being a little on the brittle side at the upper end of the tolerance. When it comes to the AR platform, bolts are probably the only part of the entire gun where I must admit to being a little bit of a brand snob.” David O’N.
[Editor’s Note: Actually Carpenter Steel does not make AR bolts. They are a steel supplier, and yes Carpenter did develop the original C-158 steel for AR bolts. Here is a contrary view, claiming that AISI 9310 Steel is actually stronger than milspec Carpenter C-158: 9310 Steel for AR Bolts.]
“Dry bolt and carrier shouldn’t cause that. Looks like a big pressure spike. What kind of ammo…?” Guy G.
Reply from Dennis: “55gr factory ammo. Piles of it.”
“Is that the new two-piece bolt everyone’s been talking about LOL?” — Darren R.
“Let me guess…the PD called you in cause they didn’t know why it stopped going ‘pew pew’?” — Jim O.
Reply from Dennis: “I was there today for qualifications. It broke during the rifle phase. Simple enough to fish the bolt parts out of the action. The training didn’t miss a beat. I have an armory full of the things.”
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Tags: AR Failure, AR-15, Dennis Santiago, Kaboom
When a “hole” is the most highly stressed part of a design…..
As a now-retired military “gum plumber”, I see this fracture as not entirely surprising.
If nobody keeps tabs on the approximate round count for small arms, especially ones used for “training”; course, after course after course, things will go awry.
Detailed cleaning? Routine examination by dedicated and qualified technical personnel?
ONE small rust pit inside that “hole” and that is the beginning of a stress riser. It is likely that when someone competent takes a look at the break surfaces, there will be clues.
A worn cam pin will load the bearing surfaces of the “hole” differently and the thin webs of the hole will start to “flex” on a micro scale; NOT a good look.
To me, there seem to have been “oversight / errors” all the way up the food chain, from the shooter to the armoury management and beyond. Checking the serial numbers in and out of the armoury does not constitute a maintenance programme.
Yeah, stuff breaks, well-designed stuff breaks less catastrophically for the operator;…….. mostly.
“Training pool” equipment, be it weapons, vehicles, radios, etc, are a good place to study “human behavior”.