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[ARCHIVED THREAD] - My new 762x39 AR has a ammo problem

Posted: 10/26/2012 9:49:37 PM EDT

So I finally finished building my 762x39 AR. All along I have been researching the problems everyone has had with that caliber in the AR world. So with brown bear ammo everything runs like a top with no problems. Then I go to try wolf ammo I had laying around and it fires one shot. It seems as if the wolf ammo does not have enough power to throw the bolt back all the way. It will stovepipe or barely eject the first round and not strip the second. I know what some of you are thinking just use brown bear ammo on. Well the idea of the build was to build a AR that wouldz eat oany thing I s should I look into using a lighter buffer spring? Any ideas would be great.

Posted: 10/27/2012 1:02:17 AM EDT

[#1]

Quoted:
So I finally finished building my 762x39 AR. All along I have been researching the problems everyone has had with that caliber in the AR world. So with brown bear ammo everything runs like a top with no problems. Then I go to try wolf ammo I had laying around and it fires one shot. It seems as if the wolf ammo does not have enough power to throw the bolt back all the way. It will stovepipe or barely eject the first round and not strip the second. I know what some of you are thinking just use brown bear ammo on. Well the idea of the build was to build a AR that wouldz eat oany thing I s should I look into using a lighter buffer spring? Any ideas would be great.

May I ask what type of buffer, buffer spring, and gas system length is on the gun?

I would say start with a Standard Carbine buffer first

Posted: 10/27/2012 4:41:36 AM EDT

[#2]

It is a standard carbine buffer and spring. The gas system is a mid length.

Posted: 10/27/2012 5:46:07 AM EDT

[#3]

The 7.62x39 will never work in an AR. Ha. Just kidding. That's what you'll read on here a lot anyway.
Could be that your gas port is partially blocked. Check your alignment of the gas-block to the port on the barrel. If it's not lined up correctly, you won't get enough gas down the tube. Who's barrel is it? Some mfgs are porting the barrels a little larger to minimize that possibility.

Posted: 10/27/2012 7:26:47 AM EDT

[#4]

Were the first cartridges you fired lacquer coated? If so clean the chamber.

Try a single shot with a magazine inserted. Does the bolt lock back?

If it still "Stove Pipes" on a single shot it is probably a gas issue.

Is the gas block aligned? Is the barrel dimpled under the screws?

A back wards hammer spring can drive you crazy (Been there)

You'll love it when it works.

Jack...

Posted: 10/27/2012 9:27:43 AM EDT

[#5]

Quoted:
Were the first cartridges you fired lacquer coated? If so clean the chamber.

Try a single shot with a magazine inserted. Does the bolt lock back?

If it still "Stove Pipes" on a single shot it is probably a gas issue.

Is the gas block aligned? Is the barrel dimpled under the screws?

A back wards hammer spring can drive you crazy (Been there)

You'll love it when it works.

Jack...

Agree with Kacee, this is a first step along with the other advice. Although you could still have a gas tuning issue once you start adding rounds to the magazine if you are on the ragged edge.
Those first two steps are a do not pass go. Clean the chamber and the bolt group very well, check the size and alignment of your gas port, go from the above test to one with additional rounds in the mag, stop and check in if you repeat the failure.

Posted: 10/27/2012 9:51:41 AM EDT

[#6]

If you want to use weaker ammo and you find the port in the barrel and gas block is lined up you may need to drill out the gas port in the barrel to a larger size. .101-.106 is pretty normal on a mid gas 7.62x39.

Posted: 10/27/2012 11:49:52 AM EDT

[#7]

All I've run in mine thus far is Wolf. Zero problems. Carbine length with standard carbine buffer. I am running the enhanced firing pin.

Posted: 10/27/2012 2:43:28 PM EDT

[#8]

I have a Kies 18" barrel. I also added the enhanced firing pin to rule out any issues there. As for the gas block it is on the money. I removed it to check and see. Like I mentioned the brown bear ran through just fine. I shot three 30 round clips of it. I think the wolf ammo does have lacquer on it. Also the bolt does lock back with the brown bear but not wolf.

Posted: 10/27/2012 3:25:28 PM EDT

[#9]

Try shooting some Wolf out of a COLD, CLEAN barrel. If it still stove pipes'
you're under gassed for the Wolf. The next move is up to you, but I would try to
obtain some gas port dimensions for a middy.

Jack...

Posted: 10/27/2012 3:39:49 PM EDT

[#10]

My Armalite won't shoot Wolf without the suppressor.

Posted: 10/27/2012 5:05:33 PM EDT

[#11]

Sounds undergassed.
pressure is much lower on the 7.62x39 than 5.56 nato. Middy gas system on a 7.62x39 might take a few trys to run with everything, carbine gas system would have been easier to make it run with everything.

Your using the best buffer for it already, and as mentioned before increasing port size will probably do it. You could also try adding a muzzle device that would add a little back pressure, im thinking Noveske pig for example.
Good luck!

Posted: 10/27/2012 7:28:39 PM EDT

[#12]

Does any one of an accurate way to check the gas port size?

Posted: 10/27/2012 7:40:39 PM EDT

[#13]

Quoted:
Does any one of an accurate way to check the gas port size?

Generally, using pin gauges is the most accurate way to measure the hole diameter
for the gas port...

Posted: 10/27/2012 8:39:40 PM EDT

[#14]

Providing I find a set of pin gauges. On a mid length 762x39 what would be the optimum size?

Posted: 10/27/2012 9:31:31 PM EDT

[#15]

What's wrong with a set of numbered drill bits?

We're not talking rocket science here. I would see what
fits, then go up the next size. It's going to be trial and error.

Even if you go wild and really over do it the worst can happen
is you'll be into an adjustable gas block.

Jack...

Posted: 10/28/2012 7:32:40 AM EDT

[#16]

I also have a Kies 18" barrel, but with a carbine gas system, that will not cycle Wolf ammo. It like just about everything else except some really old Chinese copper-washed stuff I have. Lead round nose give me some grief, but it's with failure-to-feed because it hangs up on the feed reamps. The instructions that came with my barrel warned about inconsistent function with different ammo. My first magaizine (ProMag) was also a big problem and had to be modified to work at all. I switched to ASC and feeding problems were much less.

Posted: 10/28/2012 7:55:11 AM EDT

[#17]

Quoted:
What's wrong with a set of numbered drill bits?

We're not talking rocket science here. I would see what
fits, then go up the next size. It's going to be trial and error.

Even if you go wild and really over do it the worst can happen
is you'll be into an adjustable gas block.

Jack...

Nothing wrong with using a numbered drill bit set from a size #50 to a size #31 which would give you a
good range for AR gasport sizes that would be a "poor mans" way to get a rough/overall estimate on
your gasport diameter etc.

Most AR gasport diameters run from a low of .063" to a high of.121", Including those from SBR barrels
and those from non .223 caliber bores like .243, .257, .264 , .277 , .284 , .308 ,.338 , .451 , .500 etc.
It is of course also dependent on gas port location.

A really good adjustable gasblock like Syrac is like $110, even a basic JP version is over $60.

You can get a ballpark figure by using a quality digital caliper, while not the most accurate way
to measure your gasport diameter it will give you a basic understanding on your starting point.

Good Luck.

Posted: 10/28/2012 8:14:39 AM EDT

[#18]

Quoted:
Providing I find a set of pin gauges. On a mid length 762x39 what would be the optimum size?

My Son has a 18" SS Mid Gas length upper in x39mm, IIRC the gasport diameter will be in the .078" to .088" range...

Below is a basic pin guage set (website link)

http://www.zorotools.com/g/Pin%20Gage%20Sets%20Pin%20Gage%20Sets/00059730/

($53 per set plus shipping)

Good Luck.

Posted: 10/28/2012 8:44:20 AM EDT

[#19]

My carbine SBR will run everything with the gas port at .087.

Posted: 10/28/2012 7:44:15 PM EDT

[#20]

In my experience, wolf is noticeably less potent than brown bear ammo.

Posted: 11/4/2012 9:46:49 AM EDT

[#21]

Run bear ammo (not the weaker wolf/tula) and it should run fine.

Mine liked Silver and Golden bear. Never tried the Brown Bear

Posted: 11/4/2012 10:42:10 AM EDT

[#22]

Golden Tiger seems to be the most consistant with accuracy, velocity, and relativley clean burning...we will be stocking-up
with Gloden Tiger as budget permits...The brass cased stuff will be for mostly Hunting use.

[ARCHIVED THREAD] - My new 762x39 AR has a ammo problem

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