LMT Enhanced bolt failing to extract...

[556Cliff]

LMT enhanced bolt in an LMT Enhanced carrier.

Headspace checks out with the barrel which is a Colt 14.5" SOCOM M4A1 barrel.

Carbine spring with the length verified to be within the spec and an H2 carbine buffer.


So this rifle is one I built for my brother last year and it probably has less than 500 rounds through it up to this point. It hasn't had any malfunctions prior to this and the ammo used has mostly been my brother's 62gr reloads (M855 pulls) and IMI M855. However, he started to have failures to extract, maybe 4 to 5 times per 30 round magazine when he started shooting his 55gr FMJ reloads. Happens with all magazines tried so far, but so far it's only been happening with those 55gr reloads.

He's had no issues with his 55gr reloads in his other ARs. So in trying to rule out if it was his reloads or not I decided to change out just the LMT Enhanced bolt (not the Enhanced carrier) with a new Colt bolt with the copper colored extractor spring. After doing that the extraction issues magically disappeared.

After cleaning and inspecting the LMT Enhanced bolt it's completely fine with no defects to be found... Extractor looks perfect. The only thing I can figure is that the weaker spring tension on the LMT bolt has to be the culprit, but why only with the 55gr reloads? Just seems weird, but any time reloads are involved that's usually the case. :blink:

Any ideas? Does LMT offer a set of stronger extractor springs for me to try out? I'd love to keep the Enhanced bolt with this gun since it's basically the exact setup that the Enhanced BCG was designed around.

[pointblank4445]

I had similar issues develop with at least one enhanced bolt where the extractor would slip off the rim. I believe it became an issue when I was running the gun in some extreme weather/temp conditions and this might have affected timing/obduration and such but I dunno...

Got the extractor springs replaced as another member told me he had a bolt where the dual springs didn't have the same weight/strength. It seemed to work after that but at that point I was no longer shooting in the same conditions, but I went back to regular bolts and o-rings soon after so...

[556Cliff]

I had similar issues develop with at least one enhanced bolt where the extractor would slip off the rim. I believe it became an issue when I was running the gun in some extreme weather/temp conditions and this might have affected timing/obduration and such but I dunno...

Got the extractor springs replaced as another member told me he had a bolt where the dual springs didn't have the same weight/strength. It seemed to work after that but at that point I was no longer shooting in the same conditions, but I went back to regular bolts and o-rings soon after so...

Hmmm, nothing too extreme with the temperatures he's been shooting in. Mostly in the 40s lately.

I guess it might be good to order up a new set of extractor springs and a new extractor just to test it out.

[pointblank4445]

Not sure if extreme cold was a factor or not; just putting that out that it was out of the ordinary conditions and out of the ordinary issues. Correlation does not equal causation. Just noting.

[1168]

Interesting. I think they updated the springs at some point. I’ve had good extraction with both of mine, although I did wear the springs out once.

[556Cliff]

Interesting. I think they updated the springs at some point. I’ve had good extraction with both of mine, although I did wear the springs out once.

Good to note, where did you hear that they updated the springs? I actually wanted to send an email to LMT about all this, but they'd probably just want the bolt back for inspection. I'd rather just get some replacement parts and see if that corrects the issue.

And how many rounds did it take to wear out the springs on your Enhanced bolt?

[1168]

Good to note, where did you hear that they updated the springs? I actually wanted to send an email to LMT about all this, but they'd probably just want the bolt back for inspection. I'd rather just get some replacement parts and see if that corrects the issue.

And how many rounds did it take to wear out the springs on you're Enhanced bolt?

I wanna say I read it on here somewhere, but I could be smoking crack.

It was around 8,000, IIRC in a 11.3” suppressor host. Could have been more, because that bolt used to live in a 16” gun now that I think about it. Its been used a bunch since then, also. Don’t remember if I moved it to a 12.5” or a 14.5”. I’ve got a E-BCG in one of each, and I’ve never serviced the other one, except to change cam pins.

I’d have sworn I started a thread and had the approximate round count in there, but now I can’t find it. I swear I document better when I’m working vs playing.

Anyway, they seem to last longer than other extractor springs. The bolts themselves seem nigh indestructible.