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Well, the upper receiver is back en route to me. Here is the info I got from BCA.

TECH NOTES:

FAIL TO CYCLE DUE TO GAS PORT UNDERSIZED

ENLARGED THE GAS PORT TO THE RIGHT DIAMETER

TEST FIRED 10 ROUNDS WITHOUT ANY MALFUNCTIONS

GLOBAL ORDNANCE 7.62X39 122GR FMJ
 
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Well, the upper receiver is back en route to me. Here is the info I got from BCA.

TECH NOTES:

FAIL TO CYCLE DUE TO GAS PORT UNDERSIZED

ENLARGED THE GAS PORT TO THE RIGHT DIAMETER

TEST FIRED 10 ROUNDS WITHOUT ANY MALFUNCTIONS

GLOBAL ORDNANCE 7.62X39 122GR FMJ
It would be interesting what it measured out to be and what size they enlarged it to.
 
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Well, the upper receiver is back en route to me. Here is the info I got from BCA.

TECH NOTES:

FAIL TO CYCLE DUE TO GAS PORT UNDERSIZED

ENLARGED THE GAS PORT TO THE RIGHT DIAMETER

TEST FIRED 10 ROUNDS WITHOUT ANY MALFUNCTIONS

GLOBAL ORDNANCE 7.62X39 122GR FMJ
Cool!!! maybe Hooyah DeepSea can turn his paperweight back into a functioning barrel. ;)
 
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Yeah, that would be cool. I'm not sure it would work, even with a larger gas port as I believe the 7.62x39 produces more gas than .300 blackout. But it is definately worth a try. I'll need to see the numbers.
It would make a world of difference if the mfg undersized the port in the first place. 7.62 would need an absolute "minimum" .088, but .091-.093 would be preferrable... and .125 wouldn't hurt my feelings to allow more ammo type options.
 
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Just measured . . . , .120 and it didn't work. So, still a paperweight until I can think of something else.`
Intesting. If not, you may have issues somewhere else in your gas system or in the chambering because folks are running 10.5" 7.62's successfully all over the place. I don't own one, but I've shot one myself.
 
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Oh, I have a 10.5" 7.62, it's just a pistol length system, and runs like a champ. But, apparently with a carbine length system, the 7.62x39 works but the 300 Blk don't. So, the obvious response is that the Rooskie round puts out higher gas pressure.
 
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That's the SAAMI 'standard, but not necessarily what 'my loads' are putting out. Anyway, when I first built the gun, I tried several loads and then with a can, and then with a piston system, and then with the piston and a can . . . Nothing seemed to help. Then a friend told me that 300 BLK in barrel lengths of 10.5 and shorter needed the pistol length system. So, after picking up a new barrel I've never had an issue. And, for what I paid for the first barrel, it isn't cost effective to relocate the vent or rechamber to 7.62x39mm.
Maybe it's a pressure issue, or maybe it's a volume issue, or maybe it's a pressure / volume combination issue; beats me.
 
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I have a 10.5" Davidson defense upper that's been a Pain in my bubblegum. First thing I needed to correct was ignition. Wolf extra power spring and red x enhanced firing pin fixed sporadic ignition and I now have 100% ignition with Russian garbage ammo. Second issue was short stroking. Checked for leaks, checked alignment and all good. tried different buffers no dice. For some reason they used a midlength system on a 10.5" barrel...couldn't tell you why. I measured the gas port at 0.81...undersized so I reamed it out to 0.118. One thing that should help is a krink style flash hider. Specifically the 4 piece with the internal cone. It's like 2.5" and heavy but I already have a heavy barrel and the flash with an A2 on it makes it just about worthless even in the day time so for me the krink flash hider is worth it. An enlarged gas port, adjustable gas block (so it's not ridiculous with brass), a krink 4 piece and an H2 buffer with carbine spring and presto.

I don't recall seeing elsewhere in the thread if you checked for leaks. Check the gas rings on your BCG and check to make sure the block itself isn't leaking. Lube up the buffer spring and everything other moving part and give it a go.
 

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