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  #1  
Old 11-22-2013, 8:37 AM
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Default AR-15 in 7.62x39 build?

I just had a crazy idea to build one. I know Sig makes they're 556r that shoots the Russian cartridge but I'm curious what it would take to build one? Anyone done this?

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Old 11-22-2013, 9:20 AM
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The only difference from a standard ar build is the magazine, bolt, firing pin (slightly extended pin to ensure proper strikes on the cheaper ammo), barrel and mags. The mags seem to be the biggest issues but do a search as there are plenty of people here that have done this type of build and are very happy with their rifles. I'm sure you will get the "just get an ak" as answer shortly, but there are plenty of people that are happy with this option. There are barrel/bolt combos available from several makers. One of the other problem areas outside of mags seems to me trigger weight. Some issues with very light triggers have been solved by using heavy spring/hammer combos. Hope this helps
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Old 11-22-2013, 9:24 AM
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any reliability issues with these builds anyone?
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Old 11-22-2013, 9:37 AM
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Interesting. Thanks for the info. It gives me something to go off at least. Hopefully someone who has done one on here had insight to add

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  #5  
Old 11-22-2013, 9:54 AM
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re: reliability

Keep in mind the AR-15/5.56 design has been around for half a century. There's been a lot of time to shake down this platform/round combination and it is very reliable.

The AR-15 was not designed to shoot the 7.62x39 round, BUT it is a very flexible design and can be adapted to a very wide array of cartridges with a bit of patience and tinkering. A factory design such as the SIG mentioned in the OP I would expect to be very reliable. A "home build" may require some tinkering to get the reliability where you need it to be. A lot of people who have just slapped together builds and had them "just work" on 5.56 guns, lose patience at this point when it doesn't "just work" the same with 7.62x39.

I built one, and it had some issues. I patiently researched and worked through the issues - and had a bit of help from the CalGuns family here in going through that process. Without that help.... who knows, I may have shrugged, given up, and retired it to the back of the safe. With a bit of patience and help, it has become my go-to gun. I have several 5.56 guns but I like the x39 the best. It just works for me, after a proper courtship that is! In my case it was (of all things!) the firing pin HOLE. That's right, it was the HOLE in the bolt face that was mucking up the works. On my bolt, this hole was machined with a very sharp edge - resulting in something called popped primers. The east-european primers (Wolf, Tula, etc) are soft brass material that deform against the bolt face during firing, and pressure causes the FP hole to stamp out the primer material like a cookie cutter. This is different from a PIERCED primer - which is caused by the firing pin perforating the primer. The difference is that with a popped primer, a small brass disk gets blown back through the firing pin hole into the firing pin channel. Here, it bounces around during repeated firing, and alternately jams the firing pin or allows it just enough clearance to make a proper strike. It was maddeningly intermittent and difficult to figure out until some bright soul here pointed me in the right direction.

That's just one example of the kind of issue you may have to work through. But I can say that my patience has been rewarded, and I enjoy shooting my x39 AR greatly now. If you have a short attention span and are unwilling to work with a gun over a period of time and commit to getting it working right, this build may not be for you.
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Old 11-22-2013, 10:12 AM
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I built one and really like it. Mags are indeed a challenge, but with enough research, you can track down ones that actually feed more than 5 rounds at a time reliably. Further, ammo is significantly less expensive allowing you to spend more time on the range. Don't worry about all the "corrosive ammo" nonsense either. So long as you the kind of shooter that cleans up after ever trip to the range, you'll have nothing to worry about. Have fun.
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Old 11-22-2013, 3:29 PM
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It's on my wish list
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Old 11-22-2013, 6:38 PM
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I "had" issues with the AR47. ASC mags were reliable with 5-6 rounds, and CMags were hit and miss unless I held them just right. After MUCH tinkering, I found that the feed ramps were where I was having the feed hang ups. I dremeled and polished them a little bit, and now I can stack every mag to its capacity and the rifle runs flawless. Even with Wolf
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Old 05-11-2019, 2:32 PM
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More information on "popped primers"

https://murraysguns.com/popped-primer-problems/

This can affect any x39 gun... AR, AK, or SKS.
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Old 05-11-2019, 2:33 PM
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didnt sig just announce the 7.62 conversion for the MCX.

IMHO if you want an 7.62x39 ar look into the PSA stuff or Stag so you can use proper 7.62 mags AR magwells are too straight to reliably work.
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Old 05-11-2019, 6:04 PM
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Mags are an issue on some, but it can be fixed with about 5 cent of banding material and a couple of minutes. There is way too much slop between the follower and the front of the mag. You use the banding material as a shim. This prevents the top of the bullet from going too far down and catching the mag when it is hit from behind. The awkward shape of the 7.62x39 is what contributes to the downward push. My .264LBC and x39 are both extremely reliable. I have pictures of the fix somewhere if anyone is interested.
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Old 05-12-2019, 9:12 AM
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Quote:
Originally Posted by Bisley View Post
Mags are an issue on some, but it can be fixed with about 5 cent of banding material and a couple of minutes. There is way too much slop between the follower and the front of the mag. You use the banding material as a shim. This prevents the top of the bullet from going too far down and catching the mag when it is hit from behind. The awkward shape of the 7.62x39 is what contributes to the downward push. My .264LBC and x39 are both extremely reliable. I have pictures of the fix somewhere if anyone is interested.
Yes, please.

How about grinding and chamfering the front lip of the mag body to prevent the bullet tip impinging / catching?

My first outing with a Barrier Defense Upper and ASC (10 and 20 rnd) Mags was beset with numerous malfunctions, but it was probably due to a strap on brass catcher that kept moving and preventing proper ejection

Last edited by rmnc3r; 05-12-2019 at 9:22 AM..
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Old 05-12-2019, 6:46 PM
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Quote:
Originally Posted by rmnc3r View Post
Yes, please.

How about grinding and chamfering the front lip of the mag body to prevent the bullet tip impinging / catching?
Yes, I did that too.



OK, now you have to look carefully, but you will see a gap between the front of the mag and the follower. It is actually quite substantial. What this gap does is allow the front of the follower, even long ant-tilt followers, to push down in the front before hitting the mag where it proceeds to stop dipping down. This allows the front of the cartridge to dip low enough to hit the mag. Grinding the front of the mag helps, but this fix is so cheap and easy, not to mention it cures almost all fail to feeds that I can't see why one wouldn't do it.





Now what you do is take a simple piece of banding material, you know, the kind that is used to strap stuff to pallets and place it in between the gap. It is a perfect fit and makes it tight enough to allow the follower to move up and down the mag but NOT allow the follower to tilt.





Notice how nice and tight the fit is now? I couldn't believe nobody had ever figured this out before.



There are a couple things you MUST know though. If you make the shim shorter than the ground down lip in the the mag it can slide up and block the tip of the bullet. You must either glue it to the front of the mag OR, my preference, take care to make the shim the exact same size of the front of the mag AND put a ground down notch in the shim as well. you will have a U shape in the middle with two little points on each end to still catch the corners of the mag and hold it in place.



In other words, the yellow part would be your shim in this picture extending all the way to the floor of the mag.



And if you cant find any banding material on pallets at work I will be happy to send a few strips if needed. We have rolls and rolls of new banding material in addition to what we constantly receive on pallets.

Hope I have explained it well enough, and hope it works as reliably for y'all as it does for myself.


Oh, almost forgot, this works great on the 6.5 Grendel as well as it is the parent cartridge.
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Old 05-13-2019, 11:13 AM
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Nice! Thanks for the Gunsmith's 'Kink' (Brownell's ref here) Mr. Bisley

I work in an I/C Complex but haven't seen steel banding in a long time (all Vinyl now).

Last edited by rmnc3r; 05-13-2019 at 2:26 PM..
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Old 05-13-2019, 9:31 PM
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I work in an iron shop. Mostly crane systems for me now, but was mostly structural for many years. I see all kind, metal banding, vinyl banding, fiber banding, twisted wire, you name it. I'm sure you can find something to give you the same shimming affect. This just happened to be the perfect width and thickness already. Like I said, if you want to pm me somewhere to send it I would be more than happy.
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Old 05-13-2019, 11:02 PM
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Quote:
Originally Posted by Howie44 View Post
I "had" issues with the AR47. ASC mags were reliable with 5-6 rounds, and CMags were hit and miss unless I held them just right. After MUCH tinkering, I found that the feed ramps were where I was having the feed hang ups. I dremeled and polished them a little bit, and now I can stack every mag to its capacity and the rifle runs flawless. Even with Wolf


This right here is the most important AR47 advice. Standard M4 feed ramps do not play nice with x39 ammo. Dremel and smooth out that middle hump to create basically one wide, smooth ramp and most of the time all your problems are solved.

Another common AR47 problem is under gassing. Generally you need a short gas system running wide open for reliability.


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  #17  
Old 05-15-2019, 12:29 PM
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Old Thread Earlier Thread on the issue
https://www.calguns.net/calgunforum/....php?t=1497026

Beside Mag mods, grinding the feed ramp, removing the m4 split and blending into 1 yuuuge channel seems to be helpful


Last edited by rmnc3r; 05-16-2019 at 7:09 AM..
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Old 05-15-2019, 6:54 PM
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Quote:
Originally Posted by rmnc3r View Post
Old thread on the issue
https://www.calguns.net/calgunforum/....php?t=1497026

Beside Mag mods, grinding the feed ramp, removing the m4 split and blending into 1 yuuuge channel seems to be helpful

Your "old thread" dates to 2018.

This thread has arisen from the dead, having begun in 2013!
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Old 05-16-2019, 7:06 AM
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Quote:
Originally Posted by God Bless America View Post
Your "old thread" dates to 2018.

This thread has arisen from the dead, having begun in 2013!
Ok ok; somwehat misstated - "Earlier Thread"

Better?
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Old 05-17-2019, 8:22 PM
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Quote:
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Ok ok; somwehat misstated - "Earlier Thread"

Better?
I was poking fun at the necropost, not your link.
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