Bought my first AR - NEA in 7.62x39
- Thread starter TheWhole9Yards
- Start date
I have my doubts as to a headspacing issue.
The weakest link in the 7.62x39 is the bolt lugs themselves. They usually fail first. To see the bolt lugs intact and the barrel extension in pieces is a faulty extension.
Seeing the primer missing tells me the load was excessive or it ejected the same time the barrel extension blew apart.
The weakest link in the 7.62x39 is the bolt lugs themselves. They usually fail first. To see the bolt lugs intact and the barrel extension in pieces is a faulty extension.
Seeing the primer missing tells me the load was excessive or it ejected the same time the barrel extension blew apart.
** Left: Round #5 ** Center: SKS fired from same batch for comparison ** Right: one of #1-#4 (they're all identical) **
**Same arrangement as previous photo**
Looking at those pictures I'm inclined to suspect the barrel extension. Something was up with that, being poor material or heat treatment. Look at it this way. Standard AR-15 in .223 caliber generates 55,000 PSI of pressure, if it's 5.56 round in 5.56 chamber, the pressure rises to 60,000 PSI. 7.62x39 round typically runs on 40,000 PSI with the maximum of 45,000. So while the inside diameter of the bolt itself has been enlarged a bit to accommodate the 7.62 which is a little bigger in diameter than 5.56, the outside diameter of the bolt and consequently the diameter of the barrel extension is the same, yet in case of 7.62 it actually handles lower pressure. I would doubt the naturally weakened bolt(due to bigger inner diameter) has anything to do with it, the problem should be with the extension. The 7.62 round is also known for having limited case capacity and as such it is difficult to to play with hand loads to achieve higher velocity so while not sure about possible hot load in one cartridge, the cartridge itself is rated by C.I.L. up to 51,488 PSI. If this was exceeded, there should be some visible damage on that cartridge.
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Doesn't matter what firearm it is as incorrect headspacing is a prelude to failure as well as over pressure. A chain of events with a number of items can lead to a catastrophic failure in any gun. Poor or fatigued metal, overpreassure do to cheap bulk ammo and headspacing with a small or large gap and or a combination of each.
Regardless of the make guns just don't come apart.
Regardless of the make guns just don't come apart.
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If it was only a premature failure of the barrel extension the cartridge case would not have these signs. Having the lugs torn off would not pull the primer out of the case as These military berdan primers are tightly seated and moisture sealed.
A number of things can create overpreassure. Improper quality control during the manufacture process with an incorrect powder charge, over crimping or incorrect cartridge overall length and poor or aged moisture sealant.
An operator can affect the cartridge by dropping it onto the floor or ground and inadvertently pushing the bullet deeper into the case changing the COL. Some shooters will experience a fall to feed and will clear the failure and reuse the cartridge not realizing the bullet has been pushed dangerously into the case. On next cycle " boom".
IMO bulk ammo is risky and I bet that the majority of AR failures are while using steel cased bulk.
A number of things can create overpreassure. Improper quality control during the manufacture process with an incorrect powder charge, over crimping or incorrect cartridge overall length and poor or aged moisture sealant.
An operator can affect the cartridge by dropping it onto the floor or ground and inadvertently pushing the bullet deeper into the case changing the COL. Some shooters will experience a fall to feed and will clear the failure and reuse the cartridge not realizing the bullet has been pushed dangerously into the case. On next cycle " boom".
IMO bulk ammo is risky and I bet that the majority of AR failures are while using steel cased bulk.
nah, there is absolutely no reason why any rifle chambered for 762x39 would explode because it is using factory bulk ammo, or steel case or whatever other magic unicorn reason.
no reason at all, so whatever the reason for this was, its simply due to crappy manufacturing thats all.
redshooter
CGN Ultra frequent flyer
- Location
- Central Ontario
"We give you deal, you do quality control"...
Random inspection is a good idea with any ammo...my experience has been cheap ammo can have large variation in brass oal, and neck tension, never mind the other potential screw-ups.
Random inspection is a good idea with any ammo...my experience has been cheap ammo can have large variation in brass oal, and neck tension, never mind the other potential screw-ups.
I am not saying avoid all of the brands as much as some can be problematic.
http://rsi4u.org/surplus-ammunition-a-great-bargain-or-a-great-risk/
Runningfool
CGN Ultra frequent flyer
- Location
- SW Ontario
Bad factory ammo exists. I'm not suggesting ammo caused this because that would be arm chair quarterbacking. Just like saying it's simply due to crappy manufacturing is arm chair quarterbacking.
Case in point: http://www.canadiangunnutz.com/foru...oday-I-do-enjoy-picking-up-pieces-of-my-rifle
If you look closely at the photo of the inside of your barrel extension, it looks like the locking lugs were only partially engaged when you had the kaboom. There are chips taken out of the corners (circled) the lugs have to rotate past to unlock, if it was locked at all.
Assuming the cam pin went first, your bolt might have been fully forward, but not fully rotated and locked. With those corners sheared off and the bolt not rotating properly, your bolt would have been free to move backwards completely independent of the carrier.
Assuming the cam pin went first, your bolt might have been fully forward, but not fully rotated and locked. With those corners sheared off and the bolt not rotating properly, your bolt would have been free to move backwards completely independent of the carrier.
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Or The bolt may have been completely engaged and as it rotated to unlock the pressure increased exponentially and the gun failed prior to it being completely out of battery. This caused the lugs to become nicked followed by the pin failure then the barrel extension. High pressure can do nasty things to a guns action. Just a thought.If you look closely at the photo of the inside of your barrel extension, it looks like the locking lugs were only partially engaged when you had the kaboom. There are chips taken out of the corners (circled) the lugs have to rotate past to unlock, if it was locked at all.
Assuming the cam pin went first, your bolt might have been fully forward, but not fully rotated and locked. With those corners sheared off and the bolt not rotating properly, your bolt would have been free to move backwards completely independent of the carrier.
Also the sign of the cartridge head being damaged by the extractor may have been a result of the cartridge being tightly sealed in the chamber not allowing the bolt to pull it out of the chamber. Possibly do to overpreassure. Again just a thought.
After observing the posted evidence IMHO I feel it's from the cartridge. Not disputing others opinions these are just mine.
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redshooter
CGN Ultra frequent flyer
- Location
- Central Ontario
I've looked at the pics a few times and have a question I can't answer.
First, how are steel cases made, are they manufactured by wielding together multiple pieces? The case is in pretty good shape but for the primer and what looks like a place where the gas burned through.
Second, blown primers generally come from too much pressure. If I ignore all the other evidence I see what looks like a case that has a popped primer and a spot where gas burned through the rim. Has the rim been burned through? I'm pretty sceptical of my own supposition, but looking at the picture that damaged rim looks like it's got a pretty liberal (
) coating of carbon, is that the case?...full of puns today.
What happened? The strongest bit of evidence you have is the blown primer. I'm not saying a primer couldn't come out due to a bunch of out of control forces due to a part failure, just saying every primer I've blown has been from pushing the pressure playing with seating depth and over max loads.
You have to love the ATBNEA for it's quick response to this with confident statements based on nothing but opinions.
If they have stated they will fix it let them do their thing and don't get all wigged out if something doesn't happen the next day and become a thorn...well not for a week or two.
First, how are steel cases made, are they manufactured by wielding together multiple pieces? The case is in pretty good shape but for the primer and what looks like a place where the gas burned through.
Second, blown primers generally come from too much pressure. If I ignore all the other evidence I see what looks like a case that has a popped primer and a spot where gas burned through the rim. Has the rim been burned through? I'm pretty sceptical of my own supposition, but looking at the picture that damaged rim looks like it's got a pretty liberal (
) coating of carbon, is that the case?...full of puns today.What happened? The strongest bit of evidence you have is the blown primer. I'm not saying a primer couldn't come out due to a bunch of out of control forces due to a part failure, just saying every primer I've blown has been from pushing the pressure playing with seating depth and over max loads.
You have to love the ATBNEA for it's quick response to this with confident statements based on nothing but opinions.
If they have stated they will fix it let them do their thing and don't get all wigged out if something doesn't happen the next day and become a thorn...well not for a week or two.
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By the time the gas system moves the carrier back far enough to start to unlock the bolt, the bullet has already left the barrel and the pressure has been released.
While I agree that the problem could've been the cartridge, there are a number of possible other contributing factors that are probably manufacturing quality related.
Now that I think about it, if the bolt lugs chipped those corners off and blew past them on the last round, the back of the barrel extension wouldn't have blown out like that. OP said he took a charging handle to the face, which would mean the ring of barrel extension was captured and pulled back by the bolt, pushing the charging handle to the rear with it. So the chipping would have had to be caused by one of the previous rounds. If one of the other rounds caused that damage, then it's probably a sign that the barrel extension was too brittle.
While I agree that the problem could've been the cartridge, there are a number of possible other contributing factors that are probably manufacturing quality related.
Now that I think about it, if the bolt lugs chipped those corners off and blew past them on the last round, the back of the barrel extension wouldn't have blown out like that. OP said he took a charging handle to the face, which would mean the ring of barrel extension was captured and pulled back by the bolt, pushing the charging handle to the rear with it. So the chipping would have had to be caused by one of the previous rounds. If one of the other rounds caused that damage, then it's probably a sign that the barrel extension was too brittle.
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