AR15 7.62x39 extraction/ejecting issues

[Scot4ever]

First of all I appologize if I'm posting to the wrong forum, or this already has an active discussion elsewhere...I'm a newbie.
So, here goes... I built an AR15 7.62 soviet and I'm having extraction/ejection problems. First of all the only thing that would happen was when I put a single round in the chamber it'd Fire and then come rattling back to sit in the upper with an open bolt. Casing looked a little frosty so I thought it might be a rough chamber. Ground the chamber with a little valve compound on a 12 guague barrel mop. This seemed to help and I got multiple ejected cases when testing. Then it began to stovepipe the casings, so I ground and polished the chamber a little more. I was very careful not to grind/polish more than a minute or so and the chamber looks real shiny now. Tested again and ejecting cases every now and again with also stove piping. BCG locks open with one round fired when magazine in place. If more than one round in mag it doesn't feed because the fired casing gets in the way or catches the neck on the front of the ejection port wedging the BCG open and crushing the case neck on one side. Casings don't have that frosty look any longer. I also checked the gas tube and block for alignment when I originally ground the chamber the first time. Lower is new from an 80% and so is the stock and buffer tube, spring etc. any suggestions much appreciated.

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[Scot4ever]

I forgot to add, I also replaced the extractor spring with a Stronger spring and donut ring prior to grinding the chamber.

 

[DuneHopper]

Have you tried firing it without a magazine ? And was there errors that way ?

 

[Scot4ever]

Yes, it still stovepipes with no magazine. I also tried some different ammo makers. Winchester, Federal, PPU. Federal was the one that works best and cycled through for a couple of shots after I first ground the chamber.

 

[308]

With friction, it sounds like there is not enough gas pressure to pull the round out of the chamber and eject correctly. So, by reducing the chamber friction it allows the casing to move rearward a bit more, but still not enough.

IMO, it sounds like the gas port needs to be opened up a bit more. I had a similar issue with a FAL I built years ago. Opened the port up and it functioned perfectly.

 

[KalamaMark]

You may be undergassed or over sprung. If you have multiple AR's, compare lengths of buffer springs. I had a rifle length one in a carbine tube that gave me fits for a while. You might try your shortest spring and lightest buffer and see if that changes anything.

I find the slow motion camera feature on the newer iPhones to be really helpful in troubleshooting AR cycling problems. Have a friend film the ejection port in slow motion mode, and review it, and you'll get a much better idea of what is going on with your spent cartridge and why.

 

[Scot4ever]

Thanks, I'll check the buffer springs with my other ARs first to see if there's a difference and compare the buffer weights too.

 

[Velzey]

Ughh whoa there with the valve grinding compound! Whoa whoa whoa!!! Well unless its the super fine stuff and its diluted down with oil!

Is this a new barrel? Can you post up a photo of a fired brass?

As its been said, check your buffer and spring? What are you running?

But it sounds like a gas problem to me! What type of gas block are you using?

Wow sorry I asked allot of questions there....But I have worked on 100's if not 1000's of AR's over the years..

And BTW welcome to NWF!

 

[Member 34319]

I build ars for a living. I have a cheat sheet at work of the correct diameter hole you will need for any length gas system for just about any caliber. 7.62x39 usually calls for a larger hole than 556. Let me know the specs on your barrel and I can let you know if your port is off or not. Then from there you can figure out if you need to have your hole opened up, or lesson the weight in the back.

That is if your gas block is readily accessible and your able to take it off.

 

[Scot4ever]

This is a shot of some of the casings. On the left is one that came out and rattled around in the open port but was undamaged and before any chamber polishing took place. It's difficult to see but it looks a little frosted. The middle is after polish and this one ejected. The one on the right is also after polish but got slammed in the front edge of the port by the BCG coming forward. I was very care ful with the chamber when I ground/polished it. There was definitely some visible tool marks inside to begin with but is smooth now. Hope this helps. Still got to check the buffer spring against my other ARs and will post when I've done that.

 

[Scot4ever]

Hi Reno, yes I can take the gas block off tomorrow and I'll post the specs.

 

[Member 34319]

Cool. Who's barrel? Most name brands get it right, but lesser expensive companies don't always get the size correct.

 

[Scot4ever]

And I forgot to say yes brand new barrel, carbine length gas tube on a low profile gas block. Not a pinned type gas block.

 

[Member 34319]

Another thing I've learned making the 7.62x39 work on the AR15 playform is to merge the two M4 feed ramps into one big ole ugly ramp. The taper on the cartridge is the biggest feeding nightmare on a straight magwell you'll ever know. So once you fix your gas issue, your more than likely going to find yourself in a feeding issue. This will help.

 

[Velzey]

Reno911 doesn't it get old building AR's for a living? How many a day do you build?

 

[jbett98]

So what I'm hearing here, is that Mikhail Kalashnikov is getting the last laugh when we puny Americans try to build AR's with his superior Commie Bloc ammo.

 

[Member 34319]

I have .113 for a 16" carbine length gas port size on my list.

 

[Member 34319]

Reno911 doesn't it get old building AR's for a living? How many a day do you build?

Building guns for a living is pretty enjoyable. AR sales have been slow lately, so I haven't been cranking them out as much.

 

[Scot4ever]

Just took off the gas block and tried to fit the shank of a drill bit into the gas port. I can't fit a 3/32 into the port as its a hair Smaller so that means it's smaller than 0.093. The gas tube on the other hand has a 0.123 or more, size opening at the gas block. The inside of the gas block is pretty dirty too as you can see from the photo.
I got the barrel from an outfit called Deltateam Tactical out of Utah. It's not brand name. Barrel stamp says ARD 7.62x39 1/10. From the lip where the barrel narrows to accommodate the gas block its 0.2545 to the front edged of the gas port (don't know if that helps). Looks like I need to enlarge the port to begin with.

 

[Scot4ever]

I also checked the buffer spring and weight against my other store bought AR and they're exactly the same.