10.5" 7.62x39 AR Feeding issues

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RocketBoy

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Hey guys, looking for some suggestions on an issue I'm having.
I got one of the 10.5" PSA uppers from IRG. I got it to use with cheap surplus ammo. Upon more reading maybe not the best ammo to use with an AR platform. but I'm hoping maybe there's some suggestions to help it run better. I'm running it with ASC 10rnd XCR pistol mags. A lot of ejection/feed issues. I haven't been able to get through a full mag with out a problem. Sometimes 3 or 4 rounds but that's it.

IMG_2575_zpsd7qkwoup.jpg


Also sometimes the bolt hold open will grab the front of the bolt carrier instead of the bolt.
I'm not sure if that because the bolt isn't cycling fully because of difficulty extracting the spent case.

IMG_2576_zpsupyiuhl5.jpg


I've read anything from lacquered cases sticking in the chamber to the steel cases not expanding enough and carbon/debris build up on the chamber wall.
Just looking for any tips for what I should be looking for to help figure it out. Not hoping to make it into a match reliable gun but I did hope I could use the 1000s of rounds of surplus I have. I don't really want to have to go buy a bunch of European commercial stuff like Wolf or S&B just for this.

Thanks
 
If the bolt won't lock back with one round in the mag, or will occasionally catch on the carrier, then your carrier isn't traveling far enough to the rear.

Could be caused by too small of a gas port, worn out gas rings, too heavy buffer.

Given that it's a new upper the gas rings probably aren't an issue. What buffer is in it?

Edit: if it's a standard buffer, my money is on a gas port too small for that type of ammo. It looks like Czech surplus in your pics. I've noticed it seems to have less "oomph" than Chinese surplus or modern NC in my AR. Have you shot it with different ammo?
 
Just the Czech stuff. It's all I have. Another member "Andy" says his will run with Wolf and S&B but not the Czech stuff either. I was hoping there was something I could tinker with to help it run better with what I have. Next time I can take it out I an going to take some slo-motion video of it cycling to get a better look at the full motion of the bolt.
Would opening up the gas port have a negative effect on using a stronger ammo after the fact? I could probably put a piston kit on it but that's what, another $500+ I don't mind fiddling around with it. I'm getting to learn more about how these work.
 
RocketBoy said:
Just the Czech stuff. It's all I have. Another member "Andy" says his will run with Wolf and S&B but not the Czech stuff either. I was hoping there was something I could tinker with to help it run better with what I have. Next time I can take it out I an going to take some slo-motion video of it cycling to get a better look at the full motion of the bolt.
Would opening up the gas port have a negative effect on using a stronger ammo after the fact? I could probably put a piston kit on it but that's what, another $500+ I don't mind fiddling around with it. I'm getting to learn more about how these work.
Click to expand...

I had a barrel that I opened up the gas port just a hair to get reliable performance with the Czech. Didn't notice any difference when shooting Chinese.

What weight buffer is currently in the gun?

Find some different ammo and try it out before you do anything else.
 
I put the upper on a Norinco lower so whatever came with that. I'd guess a carbine weight. The rifle came with a 14.5 upper. I've never pulled it apart to look inside. I guess that's on my learning list for tomorrow.
 
A buffer would be a fairly cheap experiment.
I personally would score a box of brass cased ammo just to see if it behaves differently.
As an aside, I ran a norinco cqa lower/buffer with an NEA 7.62 upper and had no issues with a bunch of eastern block surplus. That upper had a 14.5 barrel though.
 
Try different magazines for the feeding issues. The picture looks like it's double feeding which is usually caused by crappy magazines. Not all pistol mags are reliable in all rifles. Try only putting 5 in it if you have no others you can get your hands on.
Try removing the buffer and push the rollpin out and remove one or two of the balls in there to lighten it up a little and try again. Not sure what Norinco uses for buffer weights but there should be something in there you can remove to lighten it up anyway.
Try different ammo before you drill the gas port, once you do it you can't undo it so that should be a last resort.

Good luck
 
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You guys are on the right track IMO.

I don't think it's the mag, but the inability of the lacquered Czech ammo to move the bolt back far enough. Try it a few times with just one round in the mag and if they don't all cause the mag to hold back the bolt, you have solid evidence that it's the cause.

Mine shoots copper washed Norinco flawlessly from XCR mags, but can't feed two in a row with lacquered Czech. I say either open up the gas port, or use a lighter buffer and/or buffer spring if you want to use that ammo.
 
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Would it be ok to swap my bolt carriers? The one that came with the PSA upper is a FA profile and the Norinco is an AR15 profile so it'll be lighter and easier to move.
 
Actually the FA bolt would be lighter as the profile has been cut (the one that lets the auto sear engage) while the ar bolt doesn't have a large opening between firing pin and the rear of the bcg so more metal means heavier bolt?
 
Bsand google image full auto bolt carrier. You've got it backwards. Ar15 profile has a larger cutout on the bottom of the carrier. FA profile ends at the same spot top and bottom.
Rchmontreal, I've been running the 14.5" 5.56/.223 upper for over 2 years now without a problem. Just bought the 7.62x39 upper. Reading others experiance with this upper i'm pretty sure its an ammo compatibility issue with the upper. I would just like to tweek the rifle so it runs with the cheap ammo i have.
 
it is a gas pressure issue, normal 7.62x39 has a pressure rating of 45,000-51,000 PSI and 5.56X45 has a pressure rating of 55,000-62,000 PSI.

you might have to open up the gas port on your barrel a little bit, no larger than the size of inside diameter of your gas tube, also chamfer or countersink it, so any misalignment with your gas block will not block your gas port.
 
Like everyone said more than likely the ammo, had the same issue with a home built upper.You could try a lighter buffer and non auto carrier also a tuneable buffer spring for that ammo.
 
hbean said:
it is a gas pressure issue, normal 7.62x39 has a pressure rating of 45,000-51,000 PSI and 5.56X45 has a pressure rating of 55,000-62,000 PSI.

you might have to open up the gas port on your barrel a little bit, no larger than the size of inside diameter of your gas tube, also chamfer or countersink it, so any misalignment with your gas block will not block your gas port.
Click to expand...

It would have to be measured but you would think that if a company is going to put out a dedicated x39 upper they would do a little research and drill an appropriately sized gas port. I get the impression you believe it to be drilled to the same size as an AR-15, you may be right but if it is I would be very disappointed with that company and their products.
 
After playing detective doctor with my 762x39 M43 upper from PWS [with piston] I have found that the czech stuff causes a sticky chamber. Run chinese and clean the chamber with lacquer thinner on a 308 bore/chamber brush.

-chris
 
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