AR-15 Bolt Sheds Lugs — Can You Figure Out What Happened?
Black Rifle Gone Bad…
Take a close look at this AR-15 bolt. Notice something missing — namely all the lugs? A healthy AR-15 bolt has seven (7) bearing lugs (plus an extractor hump). For all seven lugs to have sheared “clean off”, something serious must have happened to this bolt assembly. The folks at Brownells published this “lost luggage” image on Facebook to spur discussion. So, you AR experts out there — what do you think caused the problem here? Was it over-pressure, metal defect, headspace problem, gas system malfunction (or some combination of issues)? Post your theories in the comment section below…
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Tags: AR-15, Black Rifle, Bolt, Brownells, Lugs
Metal got to hot during the manufacturing of the bolt.
I dont think it locked up fully, to much headspace on the case?
somebody was cleaning with Clorox. The hydrogen seeped into micro pores and caused the failure. ygiagam
Possibly super slow burning propellant ( reload?). Pressure was still too high when bullet passed the gas port. Causing the carrier to be forced rearward before the cam unlocked the bolt.
metal structure looks awful grainey almost like cast iron by the way carrier being forced back is what makes the bolt unlock and too much headspace would let it lockup easier
that bolt looks like it was made of cast metal….which can be done successfully if correct mix of metals is used,poured at correct temp,and hardening is used…
I would guess this bolt missed the heat treat operation.
Hydrogen embrittlement. heat treatment procedures not followed to the letter.
http://en.wikipedia.org/wiki/Hydrogen_embrittlement
Bad bolt metal is my guess. Could confirm this with an inspection of the barrel extension for any damage. A round over-pressure enough to shear off lugs from a good bolt would have burst the case and blown off the extractor. The extractor (being of a different piece of metal) appears to have been deformed by running into the barrel extension lugs but didn’t break.
My last guess
split case
Zippy might be right. The bolt and carrier in the picture appear to be plated. Bad electro-plating could cause embrittlement.
bad heat treat process
Whatever the fibrous material stuck around the ejector and other parts of the bolt was left in the rifle after cleaning and caused a incomplete lockup of the lugs. This caused point loading on the bolt and after several shots the lugs stress cracked and failed.
If you look at the extractor, the lug is burred in the opening direction, not blown straight back. So, the carrier was moving and the bolt was unlocking. A couple of questions would come up now. Was this the first shot of the day? Was more ammo from the batch shot with success? Were they reloads? From what I see, IMHO, it could just be a high pressure load. The violent opening of the bold combined with the rearward movement could easily ripe off the lugs. Great question! Happy and safe shooting!
If you look at the extractor, you see a burr in the opening direction, not straight back. So, the carrier was moving and the bolt was unlocking. A couple of questions would help, like was this the first round shot that day? Were they reloads? Was it 556 in a 223 chamber? The carrier assy being slammed back from a high pressure load could easily knock off the lugs with rotational and rearward motion. Metal fatigue or incorrect manufacture of the bolt could always be a consideration. Great question! Happy and safe shooting!
110gr Blackout might do that if it was seated deap.
300 blackout 180gr SMK fired in a 5.56 rifle is my bet. Slug completely blocks bore, 100% of gas hits bolt face with no movement of bolt to unlock – lugs shear.
Incorrect base metal or tempering process.
cleaning patch in barrel extension
Im gonna guess pistol powder.
Did someone leave another cleaning rod in a barrel?
Think you used enough dynamite there Butch…??
It looks to me like a poorly heat treated bolt. It appears that the bolt was too hard and brittle. I have seen many, many overpressure situations and every one of them catastrophically destroyed the bolt carrier, while leaving the lugs mostly intact. To have every lug go simultaneously, without affecting the carrier, I have to point the finger at metallurgy.
looks like a bolt made by a 3d printer
Cleaning patch some place
I am thinking the cam pin broke and locked up the bolt such that it could not rotate and come out of battery. The stuck bolt along with a very high pressure condition caused the lugs to shear. The fibrous material over by the ejector is interesting though; not sure what to make of it.
looks like classic bore obstruction.
previous bullet did not leave bore.
hope no one hurt.
It’s old and simple passed its life expectancy? From what I’ve been told only 1-2 fins shear. Maybe a hot load as well? What does the rest of the rifle look like?
The pock marks on the bottom right lug. Seen it before. Zinc plating not heat treated properly. Allen head cap screw 5/16-3/8″ would be tightened for a few minutes. Sometimes a couple days. All the sudden it breaks.
One day in the shop. I thought someone was messing around. Something flew by my head. It was a head of a 5/16″ allen head screw. Tightened 2 days before. checked the rest. All were cracking.
Wild guess but was this the opened up bolt face of a Grendel? If so possibly an over charged case with the weaker lugs caused lug failure .
223/556 round loaded into a 20 tactical chamber
May guess is very poor cleaning if any. The boltface and locking lugs got full of carbon from repeated firing. The locking lugs could not seat. So u have constant wear and tear.
bolt was heat treated out of spec , looks to hard. I work for a tooling company and see it all the time.
Monty C reloads….
First off the bolt is made by investment casting… very strong, very hard. I think in was caused by incomplete lock up.
So,enough already. What is the answer?
Overpressure with Direct impengement gas system, possible heat treat hydrogen embrittlement issue you cannot tell without SEM analysis. But since there is little plastic deformation on the lugs it raises suspicion.
It was from a double phase plasma gamma ray burst that was not timed to co axial movement of the higgs boson particle. That in turn fluxed the core of the parallel arc reactor which sheared the lugs.
The guess`s are in,,,whats the answer??????
obstructed barrel prior to the gas port.
My guess is that the alloy used was incorrect and/or improperly heat treated. The shear lines show pretty course grain structure.
From looks of Brass on bolt I say to much powder.
hydrogen issue was my best guess. Was the bolt or materials Made in China> They are notorious for counterfeit parts. You can’t tell what happened with one photo, we need the story and more pictures. I’m just glad I didn’t do it. Ammo and guns are too expensive to wreck. What really happened?
the bridge in San Fran has cables that were not properly treated for salt air. It would be too expensive to rebuild. Complete rebuild would be required. Not the Bay bridge but another one recently rebuilt by China and non union contracts. The relevant case is that the cables were Made in USA. Aircraft parts are often times not cleaned with the correct solvents and failures result. Did it happen here, who knows?
An illegal alien Iranian made his way here through China after studying metallurgy there for two years, got hired by mistake at the factory. Decided to start his own little jihad of his own, injected the high treat system with hydrogen and over heat treat his shifts batch causing hundreds of AR bolts to be unsafe for the American public. Watch out.
the bolt is the wrong color(silver)
Not ammo issue. If it was, upper would have most likely split. Have seen that before. Defective bolt most likely the problem
Guess the answer is unknown or more likely one of the guess`s above.
Notice that the extractor has different damage than the lugs. The extractor lug ran into a lug on the barrel before the bolt carrier rotated the bolt for release of the lockup. You can also see on the extractor a smoother damage than on the lugs. The extractor was of less brittle steel than the lugs. That proves that the bolt lugs failed before the bolt carrier retreated. The lugs on the bolt should have been strong enough to contain the case during any normal pressure in the chamber. An overpressure would have destroyed the case and no evidence of that is given. There is also no evidence given that the lugs failed on at a time. So based on what they evidence have given us, I guess that the bolt lugs failed from incorrect heat treatment.
The rifle fired with the bolt out of battery repeatedly. A patch, or part of one, was left in the breech, became entangled in the lug or the chamber, adjacent to the ejector and stayed there. Upon chambering a round, the bolt could rotate to enable the fire control but the lugs not squarely aligned. X number of rounds later we have exhibit “A” above.