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Posted: 1/23/2026 1:04:03 AM EDT
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A while back, I made a 7.62x39 upper to use and it's very accurate. I love it. But, I can't quite figure out the gassing on it. It's a 16" barrel and has a carbine length gas port. The gas port was the full .125" diameter, which as you would guess, is over-gassed. At first, it was way over-gassed. Ejecting empty cases between 1:00 to 1:30. Then I put a superlative arms adjustable block on it. Since putting the adjustable gas block, sometimes it still ejects out to 1 to 1:30 like it always did, and sometimes, it doesn't eject the empty case and tries to double feed, like it was starving for gas. I've also noticed that sometimes it doesn't lock the bolt back, again, like it's undergassed. But it's kind of completely random. Thing is, after I put the adjustable gas block on it, most of the time, the ejection is normal (when it does eject--98% of the time) but a few cases will still land at the 1' o clock. This has me thinking that I need to turn the gas up a little more because the empties may be hitting the deflector and just bouncing up to the 1 'o clock position sometimes. So, I was wanting to take the chance to ask here if anyone else has already been through this and I'm interested in reading what you may have done to remedy it. I think I'm on track with what's going on, just the crazy ejection all over the place is making me second guess myself. I didn't mention that I run the upper suppressed 100% of the time. |
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I own a couple of 7.62x39mm uppers. I had to open the port on the 20" to .125" (which is about as much as you can based on the gas tube passage) to get it to run. I use 20 round magazines which have been reliable for me. 30 round magazines, not so much. Anyone who looks at the gas port of an AK-47 is usually amazed at how large it is. Because 7.62x39mm only uses a little more powder than .223, runs faster burning powders usually and has a much large diameter bore which allows pressures to bleed off more rapidly at the port, large ports are a necessity. I would use the original gas set-up and try a heavier buffer. I'm not a fan of adjustable gas systems. |
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I appreciate all of the responses. The brass is landing about 8 feet away currently. So, I don't really believe it's under-gassed. I was just concerned that it didn't have a clear pattern to it the way most of my other calibers do. @Tony, I'll check the extractor more closely. Make sure everything moves freely and there's nothing grabbing. I also don't know whether it just has a spring or a donut insert either. Not that it matters a lot to me as long as it's working, I'm just curious what's in it. May as well peek while I'm checking the extractor. |
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Funny enough, the suppressor that I'm using on that upper, I originally made it for 300blk, and later had a change of heart and recently built the 762x39 upper and put that can on it since I never shoot 300 anymore. Being a long reflex can now instead of an integral, looks a bit goofy, but sounds good and is surprisingly accurate. |
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