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What would cause these LMT enhanced carrier fractures?

Bilb0

Bilb0

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Minuteman
Sep 16, 2023
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Dexter, Missouri
Recieved an LMT ebcg on a trade for a new 13.9" criteron core barrel.

Bolt seems to be fine but the carrier has two fractures upon inspection, says only 2500 rounds. Not confident the guy knew about this issue, but regardless;

Was curious what you guys thought may cause these type of fractures?

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It might have suffered an event before he got rid of it.

Notice that both fractures are where the thinnest wall thickness is between the bolt bore and the underside relief cuts for the cartridges/magazine feed lips. Seems like the failure mechanism propagated from inside the carrier, though there is a dent on the right fracture origin at the lip.

The enhanced LMT carrier has a conical face to it that captivates the extractor pin due to the longer telescoping length of the bolt, which is due to the elongated cam helix path. This allows the bolt to stay locked longer as the carrier momentum travels rearward, unlike a standard carrier where cam pin and bolt rotation happen quickly after carrier momentum is initiated.
 
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Is there any wear on the cam pin or cam path? Any indication on the face of the carrier where it might have been hitting the barrel extension?
 
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LRRPF52 said:
It might have suffered an event before he got rid of it.

Notice that both fractures are where the thinnest wall thickness is between the bolt bore and the underside relief cuts for the cartridges/magazine feed lips. Seems like the failure mechanism propagated from inside the carrier, though there is a dent on the right fracture origin at the lip.
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Definitely noticed the area of thinner wall thickness and that dent/chip being at that fracture as well hmm 🧐
 
msgriff said:
Is there any wear on the cam pin or cam path? Any indication on the face of the carrier where it might have been hitting the barrel extension?
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Definitely Wear on cam pin matching cam path wear. And then wear on face of carrier.
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That looks like the extractor pin was not installed flush and it was protruding out of the bolt and made contact with with the carrier.
 
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sinister said:
Cam pin and cam pin track wear are normal.

Thin part of the carrier. Add possible hydrogen embrittlement from the chrome plating and you get stress fractures. Not normal -- I've never seen a bolt carrier fail.

Call LMT and send them the same photos.
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Emailed them photos, will call first thing tomorrow n see what they say.
 
whatsupdoc said:
That looks like the extractor pin was not installed flush and it was protruding out of the bolt and made contact with with the carrier.
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I did noticed when I first took it apart the ejector pin wasnt centered and almost protruding on one side of the bolt and might not have been past flush initially.
 
TheOE800 said:
That’s ugly gouge on the face for sure.

Dude who you traded with fucked you if he didn’t disclose condition.
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Precisely 🍆. Wasn't on here. AR-15.com equipment exchange. The guy just says he didn't know. If he isn't going to offer assistance I can only hope LMT will help me out, we shall see.
 
Bilb0 said:
Definitely Wear on cam pin matching cam path wear. And then wear on face of carrier.View attachment 8342366View attachment 8342365
View attachment 8342376View attachment 8342377View attachment 8342363View attachment 8342364
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As sinister pointed out, nothing excessive in the wear. In the last two pics of your post that I am quoting, there appears to be longitudinal marks on the face cone of the carrier. Is there a pattern to those marks which would include where the fractures are? This is more of an (amateur) exercise in failure analysis, but it's still interesting to know what potential issues to watch out for.

Also, you're obviously going to replace the carrier. If you end up re-using the bolt, I would not re-use the cam pin.
 
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msgriff said:
As sinister pointed out, nothing excessive in the wear. In the last two pics of your post that I am quoting, there appears to be longitudinal marks on the face cone of the carrier. Is there a pattern to those marks which would include where the fractures are? This is more of an (amateur) exercise in failure analysis, but it's still interesting to know what potential issues to watch out for.

Also, you're obviously going to replace the carrier. If you end up re-using the bolt, I would not re-use the cam pin.
Click to expand...

Already ordered a nickel plated lwrc enhanced cam pin before doing this inspection. The highlighted green the marks on the face cone of the carrier. Circled the area that the fracture was which has more wear on the face/crown and that excess pressure on the face/crown could have stretched over to the other fracture as well, there is not enough surface area on the face to tell, the chip could have came from a pin not being installed past flush, maximizing a point of failure. I assume since it has more wear in that area that would be a greater risk of failure.
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What environment would correct this and center the wear pattern out evenly on the face/crown. A better upper reciever?
 
between the crack locations and wear on the front it looks like the result of a minor overpressure event
 
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LMT responded to the photos via email stating;

"I normally see cracks on this part of the carrier after an over pressured load or 300BO is loaded into a 5.56 chamber. That being the thinnest part of the carrier is where it cracks under the stress."
 
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Bilb0 said:
LMT responded to the photos via email stating;

"I normally see cracks on this part of the carrier after an over pressured load or 300BO is loaded into a 5.56 chamber. That being the thinnest part of the carrier is where it cracks under the stress."
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So are they going to replace it? That’s why I was watching this thread. I wanted to see what the resolution would be.

Not saying they should replace it but seeing as LMT E carriers used to be $200 and now people want $450 for them.
 
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Kadams1563 said:
So are they going to replace it? That’s why I was watching this thread. I wanted to see what the resolution would be.

Not saying they should replace it but seeing as LMT E carriers used to be $200 and now people want $450 for them.
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That was the response he gave me besides asking if I had had any failures, what ammo I used and when and where I bought the BCG.

I called and spoke to him; I was honest about the trade and my situation. He said if I was the original owner and had this situation happen they would probably replace it.

He said he appreciated my honesty and said he could probably get me a discount if I were to purchase another carrier and to email him about the discount he offered and the conversation we had on the phone.

I sent that email and have yet to get a reply. So we shall see. He was nice and carried on pleasant conversation.

Agreed; It's interesting how much they cost.
 
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Define an "over pressure" event please. Are we strictly talking about 300 blk out being fired in a 556 chamber or would a simple routine of using hot loads cause this.
 
Skeptic1 said:
Define an "over pressure" event please. Are we strictly talking about 300 blk out being fired in a 556 chamber or would a simple routine of using hot loads cause this.
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300 blk being fired in a 556 chamber. He also stated on the phone, hand loaded cartridges.

Would too powerful of a hand loaded cartridge be the same as a hot load?

He said that that area of failure is designed as a failsafe so that it gives way and fractures first rather than more catastrophic events occuring.
 
sinister said:
Cam pin and cam pin track wear are normal.

Thin part of the carrier. Add possible hydrogen embrittlement from the chrome plating and you get stress fractures. Not normal -- I've never seen a bolt carrier fail.

Call LMT and send them the same photos.
Click to expand...
Exactly. I’m sure they’ll take care of it. Hell you’d think so anyway. I know Seekins would and have on an AR10 upper that fractured where the buffer tube threads in for me.
 
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Sounds like the seller needed a new BCG and perhaps a barrel replacement, so ......

damaged BCG goes to you in trade for your barrel?
 
[
longshooter said:
Sounds like the seller needed a new BCG and perhaps a barrel replacement, so ......

damaged BCG goes to you in trade for your barrel?
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Yes perhaps a barrel as well; I noticed he had the BCG listed for $400 and then pm'd me about the new Criteron core 13.9" barrel I had up for sale and asked to trade. Would have been nice, if it was just slight wear 😂
 
Bilb0 said:
Haven't been able to find the reverse button 😁

LMT emailed back and gave me a 30% off coupon for the enhanced carrier. Carrier would come out to $155. **Head scratch

😵‍💫 Lol
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Forget LMT ! Tell dude to send back your barrel.
 
Bilb0 said:
300 blk being fired in a 556 chamber. He also stated on the phone, hand loaded cartridges.

Would too powerful of a hand loaded cartridge be the same as a hot load?

He said that that area of failure is designed as a failsafe so that it gives way and fractures first rather than more catastrophic events occuring.
Click to expand...
"designed as a failsafe"...... I am doubtful of this
 
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This sucks but I honestly don't see how this is Lmt's fault. It looks like the guy that sent it to you probably hand loaded something too hot and dumped it on you. LMT sounds like they're trying to do the best they can for you for your bad circumstance. I'd be pissed at that guy that sent it to you.
 
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ELCO82 said:
This sucks but I honestly don't see how this is Lmt's fault. It looks like the guy that sent it to you probably hand loaded something too hot and dumped it on you. LMT sounds like they're trying to do the best they can for you for your bad circumstance. I'd be pissed at that guy that sent it to you.
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Agreed. Not one to piss in anyone's Cheerios.

Guy said he's a broke college kid, and said wants to make things RIGHT; obviously in time or just temporary words. We shall see. Ill prob end up buying another carrier and forgetting. I mean it's one bad deal out of 50 deals I've had. I can't really complain .

Broke college kid buys LMT EBCG 😵‍💫
 
Bilb0 said:
Precisely 🍆. Wasn't on here. AR-15.com equipment exchange. The guy just says he didn't know. If he isn't going to offer assistance I can only hope LMT will help me out, we shall see.
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start a dispute thread. the mods there are pretty serious about sale fuckery.
 
mcameron said:
Not unheard of...that pressures got to go somewhere...

Having the carrier fail and vent all that energy out the magwell is probably the safest option.

We don't want another serbu RN-50 situation
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That clearly is the thinnest part of the bcg by design.
It wasn't designed to fail in that area though.
 
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mcameron said:
Not unheard of...that pressures got to go somewhere...

Having the carrier fail and vent all that energy out the magwell is probably the safest option.

We don't want another serbu RN-50 situation
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Was watching some serbu fail vids, that would be an ouch situation 🤯
 
Bilb0 said:
Wasn't on this site was on AR15.com equipment exchange.
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that’s what i meant. arf. you’ll win that i’m sure or he’ll get banned if he doesn’t take it back.

the mods there are serious about shenanigans. i was there for 20 years and did lots on the ee.

how long you been there and what’s your feedback score? although that shouldn’t matter much
 
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tucaz said:
that’s what i meant. arf. you’ll win that i’m sure or he’ll get banned if he doesn’t take it back.

the mods there are serious about shenanigans. i was there for 20 years and did lots on the ee.

how long you been there and what’s your feedback score? although that shouldn’t matter much
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My feedbacks 100% but only 2 on there. Just tried it out this past month
 
Bilb0 said:
Only the carrier tho $155 not the ebolt or I'd be very pleased $155 for entire E BCG haha
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I was gonna say buy a Sionics NP3 bolt but I don’t see them
Selling them separate from the entire BCG anymore


I really like my E carrier and Sionics NP3 bolt set up for suppressed use.
 
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In the op you say the bolt is fine so why can't you buy the carrier for 155 and stick the bolt you have in it?
 
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Kadams1563 said:
I was gonna say buy a Sionics NP3 bolt but I don’t see them
Selling them separate from the entire BCG anymore


I really like my E carrier and Sionics NP3 bolt set up for suppressed use.
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There is one site that sells the Sionics bolt assembly. But their out of stock. I contacted Sionics with the website link and asked if I could buy five of these from them and they said no and that they sell the full carrier with bolt assembly only. I was like huh? Lol.

Kinda sucks cause I wouldn't mind having some spare sionics bolts on standby for use with the lmt e carrier.
 
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