Comments on: When ARs Fail — Busted Bolt Incident

By: Cnarles Ast George

Cnarles Ast George — Fri, 23 Jun 2023 12:49:02 +0000

Has anyone done a simple test like doing a RC test on the bolt, case hardness and depth of case and core hordness. Fire 1000 rounds then test again and every 1000 rnds till 4000 have been fired. You will see a difference. The impingement design sends hot gasses into the bolt expansion chamber and this could start to reduce its core strength. Just a thought. Different ammo chemistry could also make a difference.

By: A. Smith

A. Smith — Sat, 09 Mar 2019 00:14:18 +0000

By looking at the finish wear on the charging handle and broken bolt, it’s a simple matter of bolt head failure after thousands of rounds in a well-known weak/failure point on the M4 design. The rifle is a semi-auto so it’s probably on the upper end of the high round count before the failure happened. Not much to do with lubing at all.Metal fatigue and high pressure after thousands of cycles.

By: Grant

Grant — Sat, 09 Mar 2019 00:09:03 +0000

The BCG and the barrel extension are the brains of the AR system. Not only do you want a bolt of the proper material spec, but it needs to be heat-treated, bead blasted and magnetic practical inspected for maximum strength/safety.

The carrier and the barrel extension should also be of the proper material.

Another critical part is the cam pin and it should not be overlooked.

What caused this failure? My guess is the material. We have no idea how many cycles the bolt has had and even with proper material, heat treat, etc…they can fail if beyond service life.

When I buy parts the entire BCG lock up parts is where I always verify quality.

By: Ed

Ed — Thu, 07 Mar 2019 13:20:12 +0000

Lloyd nailed it. Over gassing was a likely factor.

By: Joseph

Joseph — Thu, 07 Mar 2019 11:41:04 +0000

If there is friction involved, lube it. The AR doesn’t need massive amounts, if it’s evenly coated, it’s good enough. The bolt lugs, contact with cam and bolt carrier can benefit from some decent high temperature grease, but again, no need to drown the damn thing. A little dab’ll do ya.

By: lloyd myers

lloyd myers — Wed, 06 Mar 2019 18:34:10 +0000

Nature of the beast. Short gas tube = Over gassing. Chamber pressured up while bolt is trying to unlock. Adjustable Gas block?

By: Robert

Robert — Wed, 06 Mar 2019 17:09:49 +0000

I cringe when I see people hose down an AR with spray lube into the ejection port. Grease on the cam pin and a little bit of lube-de-jure on the bolt carrier rails and bolt tail, is all it needs. Hosing it down does a poor job of lubricating the things that need it, and puts lube in lots of places where it does nothing but hold onto gunk. Would you rather roll around in sand or dirt when you are soaking wet or dry?

By: Adrian Alexandrino

Adrian Alexandrino — Wed, 06 Mar 2019 15:08:08 +0000

comon prblem for handme down rifles from military

By: James Rumann

James Rumann — Wed, 06 Mar 2019 12:03:49 +0000

Can an AR run dry? Sure. Should you, no. The lube helps migrate out fouling and dirt and debris. A wet gun with dirty lube is better than a dry gun with fouling and dirt.

EDITOR: Actually excess lubrication, combined with poor cleaning practices, can be just as bad — maybe worse — than under-lubrication. We have worked with dozens of ARs. The #1 malfunction cause that we observed in semi-auto ARs was gunk in the ejector recess and the extractor pivot recess. This was a combination of lube, carbon and tiny brass particles. We suggest using the correct lube on high friction areas, cleaning the recesses “early and often” and do NOT run your gun “dripping wet”.

By: Joe Roby

Joe Roby — Wed, 06 Mar 2019 11:51:22 +0000

I tell what an old KS gun dealer would tell people about broken leaf springs in shotgun. Stop using WD40, it break those springs.