Gas rings jamming bolt

Joeyp061 · Oct 31, 2014

I have a problem I was just wondering if anyone has had. My M&P 15 is 4 mos. old. I cleaned it, lubed it up and took it out . I put about 30 rounds of 5.56 thru it. It seized up.. I mean the entire BCG froze. The armorer at the range used a rubber mallet to get it to move from the extract position. We removed the BCG.. re-lubed.. after about 15 more rounds.. Same.. I sent it back to S&W. They returned it "fixed".. I took it out about a month later and after about 30 rounds.. seized up.. I brought it home, used a mallet to get it open and after much effort removed the bolt and found the gas rings peeled back (see Pics). I have sent it back again.. we shall see what happens but ha anyone seen this before? And if so, what causes it?

Just to add.. I was using brass Federal XM193 the first time and American Eagle XM855 the second. I'm hoping they just replace the entire BCG but we shall see.

Thanks!!

ErnieDeBord · Oct 31, 2014

Wow, Ive never seen that,sure got me wondering also. What kinda ammo you using? Might go over to ar15 site, and ck around ( I sure am). Again, WOW

Rastoff · Oct 31, 2014

I have never seen that before. My first thought would be some kind of defect in the carrier.

When you get it back from S&W, thoroughly inspect the inside of the bolt carrier. Look for voids or cracks or raised defects.

A new bolt carrier group would fix it, but you shouldn't have to do that with a new gun.

uncledoggle · Oct 31, 2014

WOW! again.

Sure would be interested in learning just what caused that.

Mcwsky09 · Oct 31, 2014

That is what is referred to by industry experts as "a bad thing"

Replacing the rings should not be terribly expensive but I would look over everything very carefully.

I realize they can shift in use - but the cut in the rings are supposed to be equally offset - from the pic it looks like two of them are nearly on top of each other and the other is not far off.

gdnagle · Oct 31, 2014

Not a expert here but almost looks like the ring was smashed inserting the bolt into the carrier. I don't think you could get enough pressure from factory ammo to blow it out like that. Maybe the carrier is oversized and caught the ring inserting it.

jwalts27 · Oct 31, 2014

I have seen this in other forums with people using steel cased ammo. Not sure why

Culina · Oct 31, 2014

Inspect the inside of the carrier for obstructions, maybe the set screws for the gas key where drilled and tapped too deep.

Steve_in_PA · Oct 31, 2014

That's not caused by ammo. Gas pressure, whether it's from brass cased ammo or steel cased ammo did not cause that. Either the bolt and/or carrier is out of spec or there is a defect in the carrier.

Rastoff · Oct 31, 2014

jwalts27 said:
I have seen this in other forums with people using steel cased ammo. Not sure why

I have no doubt that you've seen people with this same problem. I also believe they were using steel cased ammo. However, it is impossible for the case of the cartridge to cause this.

This would be like saying that using a different oil filter caused the interior light to malfunction in your car.

MichiganScott · Oct 31, 2014

I've seen the gas rings bent like that when someone forced the bolt into the carrier and the ring catches on the mouth. It tends to happen if the rings and carrier aren't lubed before reassembly.

I suspect that the gun will function with a bent rig until it catches on the vent from the gas key. Stoner designed the gun such that it will run with only one ring, so running with two is not an issue.

JeffShrugged · Oct 31, 2014

I thought maybe the gas ring channel could be out of spec, giving the rings too much play. I don't see how ammo could possibly cause that. I'd say your bolt is haunted, hope you get a new one, or a whole new BCG. I know this: I wouldn't shoot it until I had it sorted out.

Joeyp061 · Nov 1, 2014

Well, it made it to Smith Wednesday. I'll tear it down when I get it back and see if I can tell what was replaced before I take her out.

LittleLebowski · Nov 2, 2014

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HalfStack · Nov 2, 2014

I'm thinking that the end of the ring was under the gas port and caught. I could be wrong but it won't hurt the position the ends away from the port like at 3-9-3 oclocks where the port is 12 oclock.

MichiganScott · Nov 4, 2014

Joeyp061 said:
Well, it made it to Smith Wednesday. I'll tear it down when I get it back and see if I can tell what was replaced before I take her out.

Let us know what the problem was even if you have to call Smith to find out.

Gas rings jamming bolt

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