7.62x39 AR build

osprey

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Well I have always wanted to take advantage of the relatively cheap 7.62x39 ammo but missed the cheap AK boat. Not really wanting to retool and learn another platform to build an AK, I have decided to build an AR upper for the cartridge. I know it has a bit of a checkered past in the AR platform with regards to getting it to run reliably but to me that is part of the allure. I love tinkering and and fixing problem guns. I understand some of the issues are mag related along with standard m4 feed ramps not being ideal for feeding properly. I am willing to endure these obstacles to get a upper that will run reliably. I am not real computer saavy but I will attempt to document some of the issues that arise and my attempts to solve them. I have never run any steel cased ammo in any of my AR's but the goal for this one is to have it run almost anything. I guess we will see if that is an attainable goal. The build will consist of an Anderson slick sided upper with a KAK 7.62x39 bcg and this barrel.
7.62X39 AR15 Melonite Hbar Barrel.

Any relevant experience anybody can share is appreciated.
 
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I own both C-product mags (2 30rnd and 1 5rnd) and ACS ( 2 30 rnd) for the AR in 7.63x39. I have had positive results with both. One of my C-product 30rnd mag's spring did get bounded up twice in one day. This happen AZ desert when it was very windy and not since, so maybe it got a little dirty? I did have a feeding issue as the ramps were not long enough. I had to extend them but nothing a little sandpaper and a quick polish couldn't fix. My buddy bought the exact same upper from the same shop and didn't have any feed issues. With your barrel, you should be better off than me if what they say is true.

I shoot steal and brass with it but I do that with most my guns. I will warn you that you won't want to shoot your .223/5.56 anymore.
 
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osprey

osprey

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I have 2 ASC 20 round mags ordered so far so that is good news. I am not sure from the description on the barrel but it sounds like it has standard m4 feed ramps. At any rate I will put it together and try to run it as is before any mods. Thanks for the info.
 
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-Make your gas port a minimum of 1/8".
-Learn to modify your barrel extension so it's a one piece feed ramp.
-The mags suck but can work. They are sensitive to how you load. Each round that gets loaded make sure the round is pushed as far back towards the spine as possible.

Edited: I forgot...The firing pin protrusion is on the light side with a standard firing pin. I recall turning the shoulder or the fillet near the front of the firing pin. I think the standard pin was only doing 0.045 protrusion don't quote me on it but you want to get closer to 0.055-0.060 by removing that fillet. Steel case has harder primers.
 
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osprey

osprey

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I got no problem with removing metal if warranted. Cut my teeth on a century Fal years ago with the double feed ramp that prevented proper feeding. Id problem and out came the dremel. That particular Fal runs like a raped ape now. Good info Max.
 
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It's an interesting beast. I helped prototype one and we learned the gas port on most barrels is just not big enough. You're not gonna hurt the gun. The pressure from a 7.62x39 is less that a 5.56x45. so bigger hole needed.

The barrel extension should be made different for a 7.62x39.
 
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osprey

osprey

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Well all my parts showed up finally and I threw down and built out the upper this afternoon. Barrel looked good but I have my doubts about the melonite finish as it looks more like a standard phosphate to me. The m4 feed ramps are the typical window peak design but they mate well with the ones in the Anderson slick sided upper. Started with lapping Anderson upper to assure barrel has even pressure on flange and stays straight. Build went without issue but had to add shim to get proper torque and line up gas tube with barrel nut that came with no name key mod hand guard. IMG_0808.JPG IMG_0810.JPG IMG_0809.JPG

Mated with a Rock River arms lower I had and she is tight. Worked bolt carrier group a few times and dry fired and checked safety function which all seemed fine. Mounted cheap millet red dot and magpul buis. Pulled some bullets out of wolf ammo and dumped the powder charge and reseated bullets to make some dummy cartridges. They seemed to cycle out of the non modified 20 rd asc mag better than the 10 rounder I carved a half moon out of the front of as the cartridges seemed to catch on the cartridge neck when pushed out of mag by hand. That may have been an unnecessary mod but we shall see after live fire. IMG_0822.JPG

Poured myself a pint of Homebrewed Russian Imperial Stout to Celebrate the grand old Russian cartridge and another smooth build. The only thing left to do is check headspace before I go test fire it. Headspace gauges should arrive this week.
.:s0090: IMG_0821.JPG
 
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osprey

osprey

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View attachment 349445
Can't tell from the picture..Did you co-witness your Red Dot with your BUIS ?o_O
If you did, you can always verify the Red Dot by flipping up your front post.;)
Why yes I did! I also put one of the de milled cartridges in chamber and let bolt carrier slam home and then test fired to make sure I had ample fire pin protrusion. It lit off primer and indent looks ample! Just an FYI there appears to be about 24.4 grs. Of a small extruded powder in Wolf military classic 124gr hp ammo. IMG_0823.JPG
 

Capn Jack

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I've got an 8 lb jug of A2220 with the loads for .223/5.56 and 7.62x39 on the label that I've
been working on, but other than that I'm still shooting the 1,000 rnds of Wolf JHP I bought
pre OB.:eek:
I had to trim my firing pin and replace the hammer spring for reliable operation with the Wolf
primers.:D

By the way...I know my front sight is on backwards.:eek:
I like it better that way.:p
 

Capn Jack

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WOW !! It may be the shading in your picture, but your firing pin certainly punched that primer.:eek:
You may want to check your first fired round for "Burn Through" :(
Then, fire a cartridge with a commercial US primer and check it too, as they're softer.;)
 
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osprey

osprey

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Yes it is plenty of protrusion for sure. I will watch for any signs of trouble during live fire. Judging by the copper witness marks left on the feed ramps and proper feeding from cycling the dummy rounds manually, I doubt I will have to take a dremel l to knock down the peak. They appear to be content following the right and left lanes and not splitting them.
 
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osprey

osprey

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Checked headspace Friday and was good to go. Went to range today and ran 100 rds of Wolf military classic 123 gr hp through her. When using 10 rd ASC mag I modified it ran 100%. Both unmodified 20 rounders were fine at 10-12 rds but spring and or follower bound up when trying to load more. Also another unmodified 10 rd ASC would not feed first round when over 8 rds was put in mag. So my impression is no mods whatsoever are needed on feed ramp or barrel gas port. It seems to be gassed almost perfect. All feed issues seem to be mag related. On the twenty rounders it seems when loading much more than 10 rds. (about where curve in mag really starts) the rounds did not have proper upward force under them and would not feed. This was very apparent as mags were loaded. I will mod other 10 rounder and probably mess with on of the 20's as well to see if I can correct. I may also try a C products mag. The really good news is this damn barrel shoots! Lots of 1" 3 shot clover leafs while dialing in at 50yds. After getting dialed in I punched out the bull with 10 rds twice once with red dot and once with the back up magpuls. At 100 yds with the magpuls I shot a 3" 5 shot group right before leaving the range. Considering my aged eyes and cheap steel cased ammo that as as good as it needs to be. Can't wait to work out mag issues and put in some more range time. I might even scope it and see how she will really group.
 

Capn Jack

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Glad to hear she's running well for you. I have a couple of the 30 rnd. CProducts mags, but I mainly use 5 rnds. in 10 rnd. magazines. I have yet to get into a fire fight at the range and shooting off of a rest, 30 rnd. mags just seem to get in the way.
 
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osprey

osprey

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Just a bit of a follow up and final synopsis after a range session this afternoon. Bought some C defense products mags to try in 10,20, and 28 round capacity. I am very pleased to report these mags ran 100% during this session of 80 rounds. They were all loaded to full capacity and unmodified so they are definitely the way to go in the ARK as I have come to call it. I would recommend them over the ASC mags. And again I experienced excellent accuracy with this budget priced barrel. I scoped it up and found it clusters three shot groups at .625-750 inches with boring regularity. I also shot several 5 shot groups that were .875-1.0625 inches. A couple 10 shot groups averaged 1.625 inches. This is all at 100 yards with cheap Wolf steel cased military classic 124 gr. hp ammo. I am very surprised at the lack of issues I had with this build and equally as surprised at the accuracy. I will be keeping this one in the stable for sure. The only change I might make is a low power tactical type optic to live on top the rail. I highly recommend a 7.62x39 upper for any AR enthusiast.
 
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I think I want to build a M4 pistol in 7.62x39, but I don't want to piece it together and fuss with it getting it dialed in.
Radical Firearms sells uppers, but I don't know anything about what's the best route. I'm looking for suggestions I can look in too.
Any help would be appreciated.
 
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osprey

osprey

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I have heard mixed results about radical firearms but do not own any of their products. It was suprising to how few problems I had with the build and function and I am building another as well. I would not expect any problems with a pistol build either. What length barrel are you looking for?
 

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