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Discussion Starter · #1 ·
Hey guys, I have a 7.62x39 failzero BCG and the extractor claw sheared off about 2500rds into it. Just thought I'd share my experience and see what you guys think caused the issue. I believe the o-ring insert created too much tension on the claw and caused premature failure. Rifle is 16" carbine gas with tuned adj gas block and lightweight carrier/buffer.
 

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That's a $20 repair. At least you didn't lose a bolt lug. Try a XP extractor spring without the o-ring next. You may not need it.
But what ronin said, Steel cased ammo in a short gas system does induce a little more stress.
 

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Discussion Starter · #5 ·
That's a $20 repair. At least you didn't lose a bolt lug. Try a XP extractor spring without the o-ring next. You may not need it.
But what ronin said, Steel cased ammo in a short gas system does induce a little more stress.
The extractor worked fine without the o-ring, I removed both it and the old spring, replaced with BCM extractor/colt gold spring. I might end up swapping the barrel to a faxon midlength. Somewhere i read that nickel boron extractors are brittle compared to nitride.
 

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7.62x39 ARs are prone to various bolt failures. It's not necessarily the manufacturer's fault.
Everything I've read said it's not only extremely common, but to be expected. In my build I've done everything to minimize stress on the bolt and components.
 

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Discussion Starter · #11 ·
How much steel cased ammo have you been using? I'd guess 100%

Steel case ammo is hard on extractors in AR format.
Almost exclusively steel cased ammo. I have a binary trigger and have been running it hard to test the function (probably 1k rounds in the past 3 months). Maybe that had something to do with it. I run that trigger so fast sometimes there's light primer strikes from bolt bounce.
 

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While everybody else was doin' the circle jerk with modified AR15 bolts to use in their 7.62x39 AR's, it was CMMG who did it right...they designed the CMMG Mk47 Mutant, which utilized their scaled down accordingly AR10 bolt/carrier design, which very effectively eliminated all the 5.56x45 to 7.62x39 bolt modification "issues".

I mean honestly, look at the difference in the bolt face dimensions between the two 7.62x39 bolts shown below; Mk47 on the left, and a modified 5.56x45 bolt on the right:



Now look at the difference in the size of the carriers; Mk47 on the bottom, standard 5.56x45 on the top:



The difference is obvious. So if you just have to have an AR chambered in 7.62x39, stop playin' around...just buy once/cry once and get yourself a CMMG Resolute/Mutant rifle or pistol - and be done with it.

Pistol:



Rifle:



 

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Discussion Starter · #13 ·
While everybody else was doin' the circle jerk with modified AR15 bolts to use in their 7.62x39 AR's, it was CMMG who did it right...they designed the CMMG Mk47 Mutant, which utilized their scaled down accordingly AR10 bolt/carrier design, which very effectively eliminated all the 5.56x45 to 7.62x39 bolt modification "issues".

I mean honestly, look at the difference in the bolt face dimensions between the two 7.62x39 bolts shown below; Mk47 on the left, and a modified 5.56x45 bolt on the right:



Now look at the difference in the size of the carriers; Mk47 on the bottom, standard 5.56x45 on the top:



The difference is obvious. So if you just have to have an AR chambered in 7.62x39, stop playin' around...just buy once/cry once and get yourself a CMMG Resolute/Mutant rifle or pistol - and be done with it.

Pistol:



Rifle:


If i didn't already have an AR10 i would have gotten a CMMG mutant. I've also had to replace gas rings maybe 1500ish rds in, some searching around the internet showed me that's a common issue with regular .223 FZ BCGs.
 

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Discussion Starter · #14 ·
FailZero was super kind in sending me a replacement extractor and advised me to do an inspection on other parts for wear. From there i discovered a loose gas key screw, so back to the factory it goes for repairs. What manufacturers would be considered a step above in terms of build quality?
 

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They are staked, either the screws weren't torqued down properly or staking was incorrect.

The screw closest to the key doesn't look staked properly. Was it the loose screw?

ETA, I've had no issues with any BCG ever but when I build my own I use Faxon or Spike's.
 
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