AR 7.62x39 failure to feed

[Hooyah DeepSea]

This doesn't surprise me, but wouldn't you rather go into a fight with something that works EVERY time . . . Actually sometimes the issue is simply a lubrication problem. I encountered that when shooting 220 gr. sub loads in my 7.5".

Anyway, as I've set up my 300 BLK Mk18 Mod 1, the pistol length gas system is 'mo betta fo you'.

 

[Member 34319]

Watching the video it's clearly short stroking. Bolt doesn't pick up another round, doesn't even clear it. Not even close. Not a feed issue if it's NOT feeding. If the rounds strip fine manually by pulling the CH and letting it go home on its own (which you do multiple times in the video), it's likely not a mag issue or feeding issue. The bolt is not getting enough gas or is too constrained to fully travel rearward. That or the gun isn't secured enough to allow counter force movement.

The anemic ejection helps me come to this conclusion. Most 7.62x39 ARs I've witnessed are so over gassed the launch brass into another county. Yours is barely getting them out.

Things to check:

Recheck your gas blocks alignment. Check your gas rings.

Things to try:

Shoulder the tube, give the gun a chance to have a solid object to counter forces against. It might be your lack of rigidity that is causing this. If you watch at 10-13 seconds in .25 speed, you'll see a cycle and a failure, take notice of the rigidity in your grip between the two shots.

It likely doesn't need much. The gas block might be misaligned by a small amount. Or everything is fine and it's just under-gassed and needs a solid grip.

Best of luck figuring it out! ARs are enjoyable!

 

[3MTA3]

A gas block dimpling jig like this one from SLR Rifleworks makes it easy to get correct gas block alignment every time. The index screw goes into the gas hole on the barrel, then you use the provided collar opposite that hole to drill the dimple(s). This is assuming you aren't using a clamp style block.

 

[FastSmitty]

Adding sights will make the gun cycle better.

Really though. Ejection looks anemic, but IT IS ejecting. The trigger is resetting so you're getting enough BCG travel to reset it, but your feeding is inconsistent. My first guess is the magazine. I've heard x39 AR mags are hit or miss, mostly miss. I'd definitely try another if not another BRAND. Next, check your gas block alignment. I suspect the reason you don't feel like you're getting "full travel" is because you're under gassed, it could be just off a touch or rotated. That 3oz buffer will travel faster than a heavier buffer, but you'll feel that velocity more. A heavier one will smooth out the impulse but requires more energy to move. something something objects at rest tend to stay at rest. So a heavier buffer would make this problem worse unless you address the gas first- assuming its not magazine related. I'd try to address BOTH.

So what exactly am I looking for on this gas block?

 

[Yarome]

So what exactly am I looking for on this gas block?

Making sure that the hole of the gas block is aligned properly with the hole in the barrel. Checking to make sure the gas tube hole in the block is aligned and not obstructed or malformed. Running a wire through the tube itself to ensure it is clean and there are no obstructions. Checking the end of the tube going into the receiver for any malformations that may be causing a gas leak between the tube and the gas key. Checking for tube alignment to the gas key of the carrier. Checking the key to ensure it is clear and securely tightened to the carrier. Checking the outlet gas ports of the key to the carrier are not obstructed. The carrier holes going into the bolt chamber. The gas rings (3 of them) on the bolt are not damaged/missing and that they are holding a sufficient seal.

When examining the barrel with the gas port loosened and moved aside, it's also good to check that the barrel is dimpled under at least one of the set screws of the gas port. The one on the receiver side of the gas block opposite the barrel port. It's not "required", but it does make gas port alignment much easier and it secures your gas block from potential rotation on the barrel.

Some of this might prove helpful.

That tool @3MTA3 noted can be very helpful for alignment and dimpling if your barrel does not have one from the mfg.

 

[Hooyah DeepSea]

In photo #2, you have the gas block up against the shoulder (where the barrel changes diameter). There needs to be a gap there, as it affects the gas port to gas block allignment. Think about the thickness of the forward handguard support that is designed to be there. So, loosen (just enough to be able to move it) the gas block and gap it with a standard paperclip, then ensuring it is vertically aligned, tighten the set screws. You can do this at the range so you can immediately test it. Once it is set and working correctly, carefully use a very little drop of blue Loctite ™ and snug it down.
Oh, and good luck; I hope that fixes the issue. Sometimes it's something that simple.

 

[Yarome]

In photo #2, you have the gas block up against the shoulder (where the barrel changes diameter). There needs to be a gap there, as it affects the gas port to gas block allignment. Think about the thickness of the forward handguard support that is designed to be there. So, loosen (just enough to be able to move it) the gas block and gap it with a standard paperclip, then ensuring it is vertically aligned, tighten the set screws. You can do this at the range so you can immediately test it. Once it is set and working correctly, carefully use a very little drop of blue Loctite ™ and snug it down.
Oh, and good luck; I hope that fixes the issue. Sometimes it's something that simple.

That's not always true of every barrel profile. If in doubt, remove your gas block completely, remove the set screws and align the gas block hole and barrel port before attempting to install it. that will show you if you need to gap your block away from the barrel collar, to what degree, if any, or mount it flush against it. The gas block hole is oversized to allow a bit of leeway.

Again.. that tool above is incredibly helpful. It aligns the dimple with the barrel port so once the dimple is in place and you set the block set screw into the dimple, it will self align.

 

[3MTA3]

Building on that - it's possible that the gas hole may not be properly aligned to the index pin on the receiver side of the barrel. With the gas block removed sight down the top of the barrel and make sure it lines up with the hole for the gas tube.

If it isn't perfect then pull the barrel nut and make sure the index pin hasn't been sheared by excessive torquing of the barrel nut. It can be repaired, but if they are not in time with each other you have a defective barrel.

This is one of many reasons I avoid cheap or unbranded barrels.

 

[Yarome]

....make sure the index pin hasn't been sheared by excessive torquing of the barrel nut.

There's a tool to prevent that too.

....but hardly worth it for a single rifle/pistol one off that a bit of care wouldn't prevent, anyway. Sure is nice though!!

Really, only the very basic of tools is "required" to service an AR platform, and there are plenty of folks willing to share how to improvise just about any task, but some tools are more equal than others and sure do make life a lot easier if you plan to expand your collection. I wish I would have started collecting tools earlier on, but had no idea AR platforms where parthenogenic.

 

[3MTA3]

There's a tool to prevent that too.

....but hardly worth it for a single rifle/pistol one off that a bit of care wouldn't prevent, anyway. Sure is nice though!!

Really, only the very basic of tools is "required" to service an AR platform, and there are plenty of folks willing to share how to improvise just about any task, but some tools are more equal than others and sure do make life a lot easier if you plan to expand your collection. I wish I would have started collecting tools earlier on, but had no idea AR platforms where parthenogenic.

A $20 torque wrench IMO is cheap insurance for a $200 barrel and they have all sorts of other applications. A wrench at that price point isn't uber accurate, but it's good enough to get you in the correct range. That and some Aeroshell, plus working the threads a bit before the final tightening.

 

[Member 34319]

You can also use a caliber to measure the distance from the shoulder of the barrel to the port and then measure the depth of the hole in the gas block from the outside edge and match the two up.

 

[Yarome]

You can also use a caliber to measure the distance from the shoulder of the barrel to the port and then measure the depth of the hole in the gas block from the outside edge and match the two up.

Better yet.... a caliper!! Calibers are too subjective.




FIFY

 

[Mike7b]

If it's a recent purchase, why not send it back to bear creek and have them fix it or exchange it for one that works.

 

[titsonritz]

In photo #2, you have the gas block up against the shoulder (where the barrel changes diameter). There needs to be a gap there, as it affects the gas port to gas block allignment. Think about the thickness of the forward handguard support that is designed to be there. So, loosen (just enough to be able to move it) the gas block and gap it with a standard paperclip, then ensuring it is vertically aligned, tighten the set screws. You can do this at the range so you can immediately test it. Once it is set and working correctly, carefully use a very little drop of blue Loctite ™ and snug it down.
Oh, and good luck; I hope that fixes the issue. Sometimes it's something that simple.

Use Red Loctite on gas block, blue isn't strong enough and should only be used on mounting screws.

That's not always true of every barrel profile. If in doubt, remove your gas block completely, remove the set screws and align the gas block hole and barrel port before attempting to install it. that will show you if you need to gap your block away from the barrel collar, to what degree, if any, or mount it flush against it. The gas block hole is oversized to allow a bit of leeway.

Again.. that tool above is incredibly helpful. It aligns the dimple with the barrel port so once the dimple is in place and you set the block set screw into the dimple, it will self align.

^^^^This. The gas block should be removed anyway and gas port pin gaged to end all the guess work. (OP, PM me if you would like to come to Oregon City and I'll do it if you don't have a set.) As far as diagnostics go, put one round in the mag, shoot it, does the bolt lock back to the rear every time? Do it a few times with quality ammo. If it is locking back reliably your gas should be OK. As far as ejection pattern goes, it may be a substandard extractor and/or ejector spring(s). For failure to feed/chamber in could be an out of spec chamber, too light of a buffer, crap mag and/or ammo.

 

[Spec.-K]

If you barrel looks like this, it's not a barrel. it's a paperweight! Sorry.

View attachment 1291921

That can be fixed...
Either tap for a jet plug, or tig weld close near the surface and re-drill.

 

[Hooyah DeepSea]

I actually considered that but the cost through my local gunsmith is prohibitive (i.e. it would cost more than buying a new barrel). But, you'll notice that I did keep the barrel, just in case! It might make a great head-whacker or something.
It's like down in California, If you carry a bat in your car; that's a weapon. But if you carry a bat, a ball, and a glove . . . That's 'sporting equipment'!! It's all in how you think about it.

 

[Member 53328]

Cause that belongs in a different platform. (Ak47)

 

[brw2]

I too have been researching 7.62x39 builds for an ar15 lower. One thing I found out is that this round DOES NOT LIKE m4 feed ramps. BCA makes their 7.62x39 barrels with 300BO feed ramps because they are wider and feed the rounds a whole lot easier. Brownells used to make their 7.62 ramps as one big ramp instead of split ramps, and it was very reliable. There are several other issues that BCA addresses in videos on their website that might help, including bolt face depth.
Also, I hate to bring up something else, but did you completely clean and lube everything before shooting it?

 

[brw2]

If it's a recent purchase, why not send it back to bear creek and have them fix it or exchange it for one that works.

I believe he wrote "Right To Bear", not Bear Creek.

 

[Yarome]

I believe he wrote "Right To Bear", not Bear Creek.

Flip that....

....It was a complete upper from Bear Creek. I said it was "Right to bear," but I did some digging and ordered the complete upper from Bear Creek Armory.

Bear Creek is typically very "budget brand". Take that meaning how you will.