AR-15 Bolt issues

[C.E.Smith043]

While cleaning my AR bolt the other day, I noticed some tearing of metal along the bolt lugs. Anyone know what causes this? This tearing is on the side of the lugs that makes contact with the lugs on the barrel extension during the closing of the bolt. All of the lugs have the tearing on them on the closing side.

The extraction side of the lugs looks fine.

 

[C.E.Smith043]

My best guess is a head space issue?

 

[Sniper338]

Ive never encountered the issue, but Ive heard headspace does that.

 

[Dusty Stevens]

was that bolt headspaced to the barrel or was this a put together rig? id be concerned about those nicked up gas rings as well

 

[C.E.Smith043]

No i dont believe so. I have 7 AR-15 uppers and have mistakenly got several of the bolts and BCGs mixed up. The reason I noticed this in the first place was I disassembled it for cleaning because I was starting to get a lot of problems with jamming. All of the uppers I have are a 5.56 chamber in them. Nothing really special about any of them they are just basic uppers from different companies that I use for hog hunting and such.
I'll put it this way, that bolt has been headspace to one of my uppers I just don't remember which one it belongs to.

 

[Rsadams]

Couldn't you get a set of go/no go gauges and get everything back in order again..?

 

[C.E.Smith043]

Couldn't you get a set of go/no go gauges and get everything back in order again..?

I agree, i really need to do that.

 

[Rsadams]

I agree, i really need to do that.

Yes sir , there's no sense in tearing up the bolts , a good one is not cheap still today... Alot of the time you can swap out a bolt for a new one with no problems but sometimes you can't... I would drag them all out and check them all.. you might get lucky and find another bolt with damage and swap them around... But it would be better to do it correctly , I know the go/no go gauges aren't exactly cheap but you get to keep them and compared to tearing up equipment , there not terribly expensive....

 

[Beau]

Is that a nitrided bolt?
Nitrided metal will chip. However, I wouldn't be too concerned unless there is a problem with the fired brass.

 

[C.E.Smith043]

Is that a nitrided bolt?
Nitrided metal will chip. However, I wouldn't be too concerned unless there is a problem with the fired brass.

I dont believe it is. Iirc, its just standard run of the mil, mil-spec stuff ive bought. Nothing fancy or unique.

 

[Knotwild]

Just asking - do you know who made the bolt? There is so much unmarked stuff out there, unless you have providence, you don't know what kind of quality you have. Does the barrel extension have any damage?

 

[C.E.Smith043]

Just asking - do you know who made the bolt? There is so much unmarked stuff out there, unless you have providence, you don't know what kind of quality you have. Does the barrel extension have any damage?

No damage to the barrel extension. The only markings i can find on the bolt say, " MPI 9310"

 

[Dusty Stevens]

Theres only a few companies that make the actual bolts. Most ive seen are pretty good quality. The rest of the parts vary wildly in quality

 

[Knotwild]

Theres only a few companies that make the actual bolts. Most ive seen are pretty good quality. The rest of the parts vary wildly in quality

That's interesting. I do know that I have seen Magnetic Particle Inspected (MPI), MPI and pressure tested, and some with no indication of either.

 

[jepp2]

While cleaning my AR bolt the other day, I noticed some tearing of metal along the bolt lugs. Anyone know what causes this?

Things you didn't state: who made the bolt? Inspection marks on it? Rounds on the bolt? What is your case head to datum when you size your brass.

I think you are just seeing some of the coating peeling off. To me it looks like a relatively new bolt.

Regarding all the comments on head space problems. If you just measure the brass coming out of the rifle, you can approximate the head space of the rifle. And if you do that for your other rifles, and start a collection of fired cases of different lengths, you can check head space using that brass after you size it without setting the shoulder back any. Just slide the BCG closed gently with your finger on the brass you are using to check.

I have head space gages and field gages for AR's, but I find just using the brass can tell you more. I have an assortment of 223/556 brass in basically 0.001" increments that I use.

 

[SG4247]

Jamming causes lots of brass and metal particles to be generated.

These particles often get in the works - between the bolt and barrel extension, bolt and cartridge, and cartridge to chamber. When this happens on a semi auto, clearances are reduced and the bolt will take a beating since the gas and spring system will attempt to force the bolt closed and open. This is somewhat common to see in an AR with lots of malfunctions.

Order a new bolt (with gas rings) check the headspace, and make sure the rifle functions without jams, and have fun.

 

[C.E.Smith043]

Thanks for the help guys. I cleaned up the edges of the bolt lugs with a small file last night and they turned out looking good. I did have some headspace problems with my brass when it originally started jamming and I think I have that eliminated now by bumping the shoulder back further. We'll see what happens on the next outing.

 

[Rsadams]

Thanks for the help guys. I cleaned up the edges of the bolt lugs with a small file last night and they turned out looking good. I did have some headspace problems with my brass when it originally started jamming and I think I have that eliminated now by bumping the shoulder back further. We'll see what happens on the next outing.

The only problem with that is you have at least two bolts mixed up out of seven rifles you own.. Creating more headspace for those two rifles will create way to much for the other rifles that are correct...

 

[C.E.Smith043]

The only problem with that is you have at least two bolts mixed up out of seven rifles you own.. Creating more headspace for those two rifles will create way to much for the other rifles that are correct...

Yea thats true. But the brass that im loading for this rifle is once fired LC and when it hits the ground it stays there. This is all stuff for hog hunting at night and i dont pick it up.

 

[gunsandgunsmithing]

That's interesting. I do know that I have seen Magnetic Particle Inspected (MPI), MPI and pressure tested, and some with no indication of either.

9310 is an alloy used in the "better" AR bolts. I would suspect you are correct about the mpi designation. The two together likely means simply mpi tested 9310 alloy.