Weird AR problem

[Draco]

My step son had a friend build me an AR for a pig gun to keep on my Mule. It is a short gun in 7.62x39. While I have killed a couple pigs with it, the thing has been a constant problem. It had 2 problems, bolt didn't go back far enough to pick the next round in the magazine every time and when it did, it lacked about an 1/8" returning to battery.

In about the 50th time looking things over, I noticed the recoil spring had been cut. It measured 9 1/4" instead of the 10" that it should. I replaced it and finally it would slam the bolt closed every time. It still wouldn't pick up the next round though and I suspect that is why the guy cut the recoil spring. One of the times I took the gas block off I noticed the gas port hole was off centered in the barrel. I checked it with a level and a center finder and it's off by almost a half a hole.

I read on line about a guy that had drilled out the gas port hole to 1/8" and used an adjustable gas block to get subs to function. I drilled out my port to 7/64" and now it functions with my hand loads but still will not function every time with military rounds.

Now my question. Should I drill the hole out to 1/8", try to angle the hole out to the side or just scrap the barrel and buy another one?

[Terran28]

First issue, not picking up the next round. Shoot 1 round only in the magazine (also try multiple mags). If the bolt does not lock back, your buffer tube is the wrong weight for that round. If it does lock back, then the bolt or the magazine is the issue on picking up the round. As for the gas hole in the barrel, it is up to you, this could also be your issue of not having enough gas pressure to blow the bolt and buffer all the way back. Save for a new barrel and tinker with the one you have. However, If you are buying a new barrel, buy a matched bolt to go with it. This in itself might correct all the issues. It is up to you, but I would try the 1 round in the mag trick first to see what the buffer and buffer spring is actually doing. Is it going back far enough? That is my .02.

[FLASH_OUTDOORS]

First issue, not picking up the next round. Shoot 1 round only in the magazine (also try multiple mags). If the bolt does not lock back, your buffer tube is the wrong weight for that round. If it does lock back, then the bolt or the magazine is the issue on picking up the round. As for the gas hole in the barrel, it is up to you, this could also be your issue of not having enough gas pressure to blow the bolt and buffer all the way back. Save for a new barrel and tinker with the one you have. However, If you are buying a new barrel, buy a matched bolt to go with it. This in itself might correct all the issues. It is up to you, but I would try the 1 round in the mag trick first to see what the buffer and buffer spring is actually doing. Is it going back far enough? That is my .02.

Good info here!


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[Easttxbowman]

7.62 are known to be finicky with mags. Get yourself a duramag and try that first.

[Mike D]

Weird AR problem

As mentioned 7.62x39 is known to be finicky in an AR platform. All parts have to be just right.

I don’t have any advice as how to fix your issue other than possibly starting with a new barrel. Depends on how much time, effort & $$ you want to put into it.


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[geezer56]

Drill it out to 0.125 in the gas port. Adjustable gas block. C- products mag. Open gas block up until the empty brass hits at 3 o'clock or thereabouts. If the bolt locks open on the last (or only) round, you are good to go. If not, try a heavier or lighter recoil buffer.

[Draco]

Thanks for the help. The bolt locks back with my reloads which are slightly hotter than military but doesn't lock back with the military rounds.

[kkp005]

What mags are you using ?

[roughneck266]

It won't hurt anything to try drilling it out to .125 (1/8"). Worst case scenario, you have to choke it down with the adjustable gas block. If it still won't do it, then a lighter buffer will likely get it the rest of the way.
As mentioned, commie rounds have been well documented as having issues with the AR platform, they were never intended for it, but once you get it working correctly it will be a good reliable rifle.

[gatorgrizz27]

I did research before I built mine, I’m well versed in AR tuning but not in 7.62x39.

The most common problems I found were mags, firing pins, and feed ramps. I bought Duramags, a Windham Weaponry firing pin, and a $100 barrel off gunbroker that I ground the feed ramps together on. I’m using an adjustable gas block, H2 buffer, and blue Springo (enhanced power) buffer spring to strip steel cased rounds out of steel mags reliably.

Other than the first batch of junk ammo (Maxxtech), the thing has run like a sewing machine. I did have to back the gas block screw out farther than I was expecting, and I didn’t measure the gas port size before installing it.

It does sound like your rifle is under gassed from the description of picking up a round with hand loads but not cheaper Russian ammo. If you’ve verified that the gas block is aligned and it’s not leaking anywhere, drilling the port out to 1/8” is probably a good call.

[Terran28]

Thanks for the help. The bolt locks back with my reloads which are slightly hotter than military but doesn't lock back with the military rounds.

Does it pick up every round of your reloads, or is it still finicky doing that? As everyone said, 7.62x39 has to be "perfect" in an AR platform. If it picks up all of your handloads just fine, it is the buffer weight and you will need a lighter one. This is why I went with a 6.5 Grendel cartridge for my AR build. I didn't like the 6.8, didn't want 7.62x39 nor 300 Blackout. I wanted a mid-range 300-500 yard gun with a flat shooting 6.5 round but in a short AR platform lower that I use for 5.56/.223 as well.

[Draco]

Does it pick up every round of your reloads, or is it still finicky doing that? As everyone said, 7.62x39 has to be "perfect" in an AR platform. If it picks up all of your handloads just fine, it is the buffer weight and you will need a lighter one. This is why I went with a 6.5 Grendel cartridge for my AR build. I didn't like the 6.8, didn't want 7.62x39 nor 300 Blackout. I wanted a mid-range 300-500 yard gun with a flat shooting 6.5 round but in a short AR platform lower that I use for 5.56/.223 as well.

My reloads have worked perfectly. The mass ammo I have is made by Geco, Hungarian I think. I went with this caliber because of cheap military for lots of practice and they had brass cases for reloading.

[imyomama]

first , if barrel shoots good , leave it alone .. second if spring is out of spec, that's a cheap fix .. better yet find a buddy who has one and just swap it to test .. should be a standard spring .. once you have a spec spring the fun begins .. if hole is not centered , make sure the block is centered to the hole .. if partially obstructed it will limit gas . if way way off the gas tube will rub on the key ... if that's the case .. barrel swap .. drilling the hole can work, and adjustable gas block can too up to a point .. mine runs flawless , unsuppressed or suppressed .. it's a 10.5" . one note , they make an extended firing pin especially for 7.62x39 that is just a tad longer to reliably ignite russian ammo with hard primers .. if you don't have issues don't worry ... you can also get the little o-ring for the extractor if you have extraction problems ... bottom line , get it back to vanilla parts first , then experiment ... don't think you gonna solve anything by leaving that spring of messing with port hole at first. my 2c.

[Terran28]

My reloads have worked perfectly. The mass ammo I have is made by Geco, Hungarian I think. I went with this caliber because of cheap military for lots of practice and they had brass cases for reloading.

I would weigh your current buffer (I think in grams) and then get a lighter one or find someone with a lighter one and run it to see what it does. It seems like the factory ammo isn't pushing the pressures that your handloads are, therefore you are short-stroking the buffer and spring and it is missing the pickup of the rounds. If you do this, be aware, you might get more slamming of the buffer and spring against the back of the buffer tube, so it may feel "harder kicking" to you with your handloads. This is my .02 and what I would do personally.

[BlessedVeteran0305]

I would start with changing out the buffer spring and if you can find a buddies AR that has that is similar, I would try to swap out the BCG and see if the problem duplicates. If it does then I would say its your gas tube not creating enough pressure. If not then I would start with troubleshooting the BCG. If you end up going this route, start by swapping out the bolt. Good Luck.