7.62x39 broken bolts

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[ARCHIVED THREAD] - 7.62x39 broken bolts

Posted: 8/11/2009 6:58:00 AM EDT

I've had two bolts break in my 7.62x39 AR in the last two weeks. In both cases the lugs on either side of the extractor broke off. The upper is a Model 1, as was one of the bolts. The other bolt was an MGI. In both cases I was shooting Wolf black box. Any ideas about what's going on and how to prevent it from happening again?

Posted: 8/11/2009 7:28:36 AM EDT

[#1]

I'm totally out of my league here, but I remember reading something about a company that removed a little material from the back of the lug opposite the extractor. I guess the idea was to spread the pain on a fewer lugs, but at least it would exert even pressure on the remainng lugs. I am not in any way at all suggesting you do this, but you might try researching this. In fact, I could totaly be making this up.

Posted: 8/11/2009 7:30:55 AM EDT

[#2]

LMT makes an improved bolt, Id look into getting on of those.

Posted: 8/11/2009 7:31:38 AM EDT

[#3]

Model 1 Sales is your problem, I'm sorry to report.

Posted: 8/11/2009 7:33:06 AM EDT

[#4]

Quoted:
I've had two bolts break in my 7.62x39 AR in the last two weeks. In both cases the lugs on either side of the extractor broke off. The upper is a Model 1, as was one of the bolts. The other bolt was an MGI. In both cases I was shooting Wolf black box. Any ideas about what's going on and how to prevent it from happening again?

Whats your round count? I have had about 3k rounds through my M1S and no problems. Really wierd.

Posted: 8/11/2009 8:09:45 AM EDT

[#5]

Quoted:
I'm totally out of my league here, but I remember reading something about a company that removed a little material from the back of the lug opposite the extractor. I guess the idea was to spread the pain on a fewer lugs, but at least it would exert even pressure on the remainng lugs. I am not in any way at all suggesting you do this, but you might try researching this. In fact, I could totaly be making this up.

You're not making it up. Armalite is the company that does this. Info on their site.

Posted: 8/11/2009 8:22:59 AM EDT

[#6]

Lewis Machine and Tool is who's bolt you want...

Posted: 8/11/2009 9:02:44 AM EDT

[#7]

I've broken DPMS, Model 1 and, Colt bolts - all in FA.

Posted: 8/11/2009 9:05:09 AM EDT

[#8]

Quoted:
I've broken DPMS, Model 1 and, Colt bolts - all in FA.

More dmps for me though

I have the LW "super bolt" that is working. The DPMS dont last long

Posted: 8/11/2009 9:10:11 AM EDT

[#9]

Quoted:
I'm totally out of my league here, but I remember reading something about a company that removed a little material from the back of the lug opposite the extractor.

LMT 7.62x39mm bolt:

User amphibian's posts made me aware of the LMT bolt; I have the impression that he's broken just about every other kind of 7.62x39 bolt out there.

My M1S bolt has been fine so far, at around 2K rounds. It's outlasted my MGI bolt by a factor of almost 2 at this point. My coming ArmaLite barreled 7.62x39 will get an LMT bolt.

Posted: 8/11/2009 9:20:46 AM EDT

[#10]

Quoted:
User amphibian's posts made me aware of the LMT bolt; I have the impression that he's broken just about every other kind of 7.62x39 bolt out there.

He has.
When amphibian says the LMT is the best, you can take it to the bank. They do, however, still need to be modified for firing pin protrusion.

Posted: 8/11/2009 10:24:41 AM EDT

[#11]

How many rounds do you think have been through it? I have about 1100 through my Model1 upper/bolt right now and it is showing very little wear.

Posted: 8/11/2009 10:51:53 AM EDT

[#12]

I've put around 1,000 rounds through the rifle. It seems significant that both bolts broke at the same place and that they were two different makes, a Model 1, which came with the upper, and an MGI that I purchased when having trouble getting the rifle to fire Wolf ammo. I continued to have ignition problems until I put a RRA match trigger in the lower, though I can't see how that would have influenced the bolt breakage. Who else makes 7.62x39 bolts? LMT doesn't list a 7.62x39 on their website, but I emailed them asking if they carry the bolt.

Posted: 8/11/2009 11:11:57 AM EDT

[#13]

LMT has the 7.62x39 enhanced bolt. I just got one for my 6.5. Nice. I've sheared a lug off a model 1 but they replaced it. I've got a DPMS that has around 2K rounds w/o problem.

Posted: 8/11/2009 11:15:14 AM EDT

[#14]

Could be your chamber is on the long side with headspace. Possibly a slightly misaligned bbl ext. I think its something besides the bolt since its happened with 2 different brands.

Posted: 8/11/2009 12:07:04 PM EDT

[#15]

LMT has "an enhanced style" 7.62x39 bolt with a "lobster tail extractor." Can anyone tell me what that means, especially the lobster tail extractor? It's pricey, but I'll go for it if it's what I need. Still, Glane5910's comment about headspace etc. has me thinking. Probably should contact Model 1 for their input (and maybe get the broken bolt replaced).

Posted: 8/11/2009 12:40:47 PM EDT

[#16]

Just talked to the good folks at Model 1 and Brandon asked me to send the upper in question to him, complete with broken bolt. He asked if there have been any reports of people having similar problems using Wolf black box, though I haven't heard of any but figured this was the place to ask. And I'm going to spring for the LMT bolt just to be on the safe side. Thanks for all the input (and any yet to come).

Posted: 8/11/2009 1:13:38 PM EDT

[#17]

I've got an AR Performance Super Bolt, but haven't tried it yet.

Posted: 8/11/2009 2:09:48 PM EDT

[#18]

Quoted:
Just talked to the good folks at Model 1 and Brandon asked me to send the upper in question to him, complete with broken bolt. He asked if there have been any reports of people having similar problems using Wolf black box, though I haven't heard of any but figured this was the place to ask. And I'm going to spring for the LMT bolt just to be on the safe side. Thanks for all the input (and any yet to come).

No problems here with Wolf BB, I shoot a mix of Wolf MC, Wolf BB and Golden Tiger usually

Posted: 8/11/2009 2:23:46 PM EDT

[#19]

Quoted:
...the lobster tail extractor?

It uses two springs.

Posted: 8/11/2009 5:25:38 PM EDT

[#20]

Yep, still running an LMT bolt in both of my 7.5" uppers in FA w/ 75 round drums.
Haven't broken one yet.

Link to Video 75 round drum FA

Posted: 8/11/2009 8:05:16 PM EDT

[#21]

Quoted:
I've had two bolts break in my 7.62x39 AR in the last two weeks. In both cases the lugs on either side of the extractor broke off. The upper is a Model 1, as was one of the bolts. The other bolt was an MGI. In both cases I was shooting Wolf black box. Any ideas about what's going on and how to prevent it from happening again?

Joe,
It could be that the rifle is over gassed and the bolt is being cammed open while the pressure is still high in the case, putting pressure on the lugs.
The pistol length gas systems are really bad, the carbine are bad depending on who built the upper and what size port it has.
You may try a steel adjustable gas block, not alum.

Posted: 8/11/2009 8:28:20 PM EDT

[#22]

7.62x39 bolts have always had a reputation for early failure. Opening up the bolt face to fit the wider Soviet round removes strength. I'd suggest you follow the advice of the more experienced 7.62x39 shooters that suggest the LMT bolt.

Posted: 8/13/2009 6:05:02 PM EDT

[#23]

Quoted:
7.62x39 bolts have always had a reputation for early failure. Opening up the bolt face to fit the wider Soviet round removes strength. I'd suggest you follow the advice of the more experienced 7.62x39 shooters that suggest the LMT bolt.

They have had their problems but that could be from other factors besides the bolt itself. The grade of steel used and the heat treatment are big variables. How many were shot peened, MPI etc? Having a barrel extension slightly out of spec could cause problems too. I'm just not convinced there is any one major player in the problem. Ammo that was over that 50-52,000 PSI limits could cause problems as well. The LMT is a very good bolt, I run it in my 6.5. I also have a DPMS that I started off with and its been great. AR performance has 7.62x39 bolts made with 9310 that should be dam near buller proof as well. I mentioned the Model 1 bolt I had sheared a lug after 30-40 rounds but to their credit, they replaced it no problem, no questions.

Posted: 8/13/2009 6:08:45 PM EDT

[#24]

Quoted:
Yep, still running an LMT bolt in both of my 7.5" uppers in FA w/ 75 round drums.
Haven't broken one yet.

The LMT Enhanced is still made, its just not in their catalog. You have to call and order it. They have less than 300 left now though.

Posted: 8/13/2009 7:28:54 PM EDT

[#25]

The LMT Enhanced is still made, its just not in their catalog. You have to call and order it. They have less than 300 left now though.

I took that picture and put that text in there over a year ago. Back then they told me they had something like over a 1000 available but were not in the catalog. They had a deal with another vendor to make them which fell through. I know people have been ordering them over a year ago and to this day as you mentioned. I never said you can't get them. Just that they weren't being made which was true back then and was still true as of the last Shot Show in Orlando (Feb 2009). I was told by one person at LMT that they still had no intentions to make them again. One of my friends spoke to someone else at LMT at Shot (same Feb 2009 Show) who told them that they WERE going to make them so who knows. I suspect they still are not making them and what they have is what is still left over from the run done a few years ago. One issue w/ the LMT is no spare Extractors. I haven't broken one yet though. I did get some spare 6.8 extractors and think I can shape it to work. Works by hand.

Posted: 8/13/2009 7:57:18 PM EDT

[#26]

Quoted:

The LMT Enhanced is still made, its just not in their catalog. You have to call and order it. They have less than 300 left now though.

I took that picture and put that text in there over a year ago. Back then they told me they had something like over a 1000 available but were not in the catalog. They had a deal with another vendor to make them which fell through. I know people have been ordering them over a year ago and to this day as you mentioned. I never said you can't get them. Just that they weren't being made which was true back then and was still true as of the last Shot Show in Orlando (Feb 2009). I was told by one person at LMT that they still had no intentions to make them again. One of my friends spoke to someone else at LMT at Shot (same Feb 2009 Show) who told them that they WERE going to make them so who knows. I suspect they still are not making them and what they have is what is still left over from the run done a few years ago. One issue w/ the LMT is no spare Extractors. I haven't broken one yet though. I did get some spare 6.8 extractors and think I can shape it to work. Works by hand.

My bad..thought the pic said no longer available, didn't pay much attention to date of pic. Correct on extractors, they have for the 6.8 but not 7.62x39. This might all change as more people get the 6.5's chambered for a standard recessed bolt. it took a month to get mine so they could very well have them stashed somewhere else. I'll try one of the 6.8 extractors, didn't think it would take much to get them to work. That's the only thing that I was hesitant about buying it.

Posted: 8/13/2009 8:21:13 PM EDT

[#27]

A 5.56 bolt has about 3600 Lbs of bolt thrust the 7.62 is 4700 put all the snake oil on them you want they will all break the system is overstressed. if you look a stoners later designs (stoner 63) the bolt is bigger
you may have to live with a 3k bolt life unless you are willing to pay for LMT

Posted: 8/13/2009 8:52:19 PM EDT

[#28]

Quoted:
A 5.56 bolt has about 3600 Lbs of bolt thrust the 7.62 is 4700 put all the snake oil on them you want they will all break the system is overstressed. if you look a stoners later designs (stoner 63) the bolt is bigger
you may have to live with a 3k bolt life unless you are willing to pay for LMT

I don't know how many rnds a standard will take if everything about it is right. I've got well over 2K on the DPMS I was running in my 6.5 before i put it up for a spare and now using the LMT. Hopefully this LMT I just put in there will last and last. One of the guys on the 6.5 forum works at ar performance. He's got several thousand rounds on a 9310 he had opened up to use on his 6.5. I'm not sure how much better the carpenter bolts are. I agree with you though they need a bigger/better bolt to last and last..and last. maybe something along the lines of the new Rem 30 AR's bolt. The LMT is probably the best choice over all.

Posted: 9/3/2009 1:42:47 PM EDT

[#29]

Why does the LMT have that groove cut into the lugs?

Brick

Posted: 9/3/2009 3:37:29 PM EDT

[#30]

For stress relief. It will allow the lug to flex instead of break off.

Posted: 9/3/2009 4:48:24 PM EDT

[#31]

Thank you. Does it also have that Armalite style trimmed lug opposite the extractor?

Thanks,

Brick

Posted: 9/3/2009 4:52:27 PM EDT

[#32]

Quoted:
Thank you. Does it also have that Armalite style trimmed lug opposite the extractor?

Thanks,

Brick

Yes, look about 10 posts down on page 1 of this thread.

Posted: 9/3/2009 5:48:35 PM EDT

[#33]

Yes, I saw that and was confused. It looks like they trimmed the side of the lug in that picture, and didn't trim the contact surface area of the lug where it would touch the barrel extension lug. Anyone understand that????

Thanks,

Brick

Posted: 9/4/2009 10:17:11 AM EDT

[#34]

Quoted:
Yes, I saw that and was confused. It looks like they trimmed the side of the lug in that picture, and didn't trim the contact surface area of the lug where it would touch the barrel extension lug. Anyone understand that????

Thanks,

Brick

That lug isn't as tall either. Is that what you're talking about?

Posted: 9/8/2009 6:48:35 AM EDT

[#35]

That lug isn't as tall either. Is that what you're talking about?

No, it looks to be as tall as the other lugs (from the breech extension side to the bolt face side). I think you are talking about its height from the base of where the lug meets the main body to its outward most extension and yes, they did shave that down on that lug but I have no idea why.

Brick

Posted: 9/8/2009 1:11:09 PM EDT

[#36]

Quoted:

That lug isn't as tall either. Is that what you're talking about?

No, it looks to be as tall as the other lugs (from the breech extension side to the bolt face side). I think you are talking about its height from the base of where the lug meets the main body to its outward most extension and yes, they did shave that down on that lug but I have no idea why.

Brick

Correct, if you look at it horizontal then its the same length. If you look at it vertically, its shorter and shaved on a portion of it forming an "L"..

Posted: 10/25/2009 3:35:27 PM EDT

[#37]

Quoted:
I've got an AR Performance Super Bolt, but haven't tried it yet.

Interesting , these use standard 5.56 extractors

[ARCHIVED THREAD] - 7.62x39 broken bolts

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