7.62x39 AR Upper?

[Mainehunter]

I have an opportunity to pick up an upper pretty cheaply from a guy at work. He toyed with it for about a year or so but couldn't to get it work right. I've done some homework and most of the problems are either the mags, the feed ramps aren't designed right or the gas port too small. Since I bought a CZ 527 in 7.62x39 last fall I'm starting to fall in love with the cartridge. He doesn't have the detail's on the kind of upper it is (thinking DPMS) but if this doesn't work out what other upper should I pick up or build my own?

Mainehunter

[Grizz]

I have an opportunity to pick up an upper pretty cheaply from a guy at work. He toyed with it for about a year or so but couldn't to get it work right. I've done some homework and most of the problems are either the mags, the feed ramps aren't designed right or the gas port too small. Since I bought a CZ 527 in 7.62x39 last fall I'm starting to fall in love with the cartridge. He doesn't have the detail's on the kind of upper it is (thinking DPMS) but if this doesn't work out what other upper should I pick up or build my own?

Mainehunter

soreshoulder has some good points about this, but until he gets here ...

the one thing I read that makes sense to me is someone took out the ridge between the m4 feed ramps. the ak isn't designed for that I guess? anyway, someone on arfcom avowed that this stopped all the misfeeds in his upper. if that makes sense. the power of dremel. the power of doing.

Grizz

[sore shoulder]

No one wants to see a 7.62x39 upper succeed more than me. I dream of an accurate 7.62x39 with a good scope and premium ammo.I've been reading about it and eagerly following new developments that are supposed to solve the problems.

That being said, in my opinion there are certain engineering issues that are nearly impossible to overcome.

The main one being magazine feeding. Because the magazine well on an AR is straight for several inches, and the tapered x39 requires a constant curve and an angled approach to the feed lips, this issue has yet to be reliably overcome as far as I'm aware. The "Frankenmags" do not have consistent reports even after years of trying to make them work. C products has probably put the most effort in to this as far as I'm aware, and if anyone could make it work, they would be the ones. The cartridge just does not like that straight approach to the feed lips. And even a 10 round SKS magazine has a significant curve/angle to it.

Additionally, the cartridge has a lot of bolt thrust when using steel cases which causes sheared locking lugs. Lugs that are already compromised due to reduced area to accommodate the larger case head.

Years ago the Army requested a rifle that could fire 7.62x39. Knights, LMT and others submitted rifles, the ones I saw all had an angled magwell and used AK or similar mags. Rock River finally built a 7.62x39 rifle in the "AR pattern" but in all completely new dimensions to accommodate the cartridge, a larger bolt/bolt face/locking lugs, and a magwell that uses AK mags.

I still plan to build one, but it will have an improved chamber and .308 barrel vs .311 to shoot what is unofficially called a 30 Grendel (there are other names I cant recall, I think one is .30 GI, the Army shooting team was using it a few years ago), and still shoot the 7.62x39 if needed, though not recommended as the slightly larger bullets cause premature barrel wear.. The straight walled brass case significantly reduces bolt thrust and has a significant increase in powder space giving it 30-30 performance in an AR15 platform.

This all brings us full circle back the the .300BLK. While I take exception to the claims it "equals 7.62x39", It's close enough, it works flawlessly, it uses all the standard AR15 parts except the barrel, it uses standard mags and you can buy ammo for it at almost any Walmart, and it makes a perfect AR pistol or carbine due to excellent performance from short barrels. As much as I wanted to build a x39, I'll be building a .300BLK first.

If you get it, please keep us updated on your progress. I'm eagerly awaiting one that works flawlessly.

[cas]

Mags generally aren't an issue if you're happy with only putting 5 rounds in them.
My experience was that around 7 they start getting funky. Another issue people run into is the cheap ammo they hope to shoot has hard com-block primers and won't fire right. Some brands are fine, some 50/50, some won't fire at all. So they end up with extra heart springs and extra crappy trigger pulls.

There's never any surprise when you see them for sale used.

[Thunder50]

Yep, mags seem to be the issue. As said, 10 rounds or less is good, but over that, not so good. Even some of the "Frankenmags" which are supposed to hold 30, won't feed if over 20 or so. AND, out of the 5 "Frankenmags" I have, only one of the will feed consistently. I don't shoot steel cased stuff thru my gun and don't have any problems with feeding/firing as long as I don't put too many rounds in the mags.

I would say to go with the 300 blackout or the 7.62 x 40 (I think LMT does that one--google it though). Blackout is more common.

[JOHNNY WACKO]

I think curved mag is it. and i use 5 or 10 rd mags in my ak because when your shooting with friends you save on free ammo to others. have not had a ar in the 39 ammo yet to find out so i will watch what others do.
i do like the 300black out and will have 1 soon.

[Mainehunter]

Thanks gentlemen for the feedback! I know that the bolt carrier needs to be swapped to accommodate the x39 case. I've read somewhere there have been reports on failed x39 bolts. They just can't take the bolt thrust and some have switched to using 6.5 Grendel bolt carrier.

It's been in the back of my mind since the holidays of building a 30 cal. or even 35 cal. upper (358 Gremlin). Besides the 7.62x39 I've also looked at 30 Remington AR but for some reason I just can't warm up to the 300 Blackout, don't know why.

I'll wait and see what this guy has to offer. I'll probably won't see him till beginning of next week.

Mainehunter

[Grizz]

from reading the thread it seems the "solution", if a 14" krinkov pistol won't suffice, is to use the AR-10 receivers and uppers, with a magwell adaptor that accomodates AK magazines.

big bolt, big magwell, with the right barrel extension, not M4, it might go together and run the x39 just fine.
it is, after all, a wannabe .308 with fat bullets.

whatcha think?

Grizz

[AJMD429]

This all brings us full circle back the the .300BLK. While I take exception to the claims it "equals 7.62x39", It's close enough, it works flawlessly, it uses all the standard AR15 parts except the barrel, it uses standard mags and you can buy ammo for it at almost any Walmart, and it makes a perfect AR pistol or carbine due to excellent performance from short barrels. As much as I wanted to build a x39, I'll be building a .300BLK first.

The 300 Blk would be my choice for 'practicality' in terms of getting a mid-power 30 caliber cartridge in an 'AR' format - even if it isn't as much 'fun' as the 7.62x39 cartridge history-wise.

The 7.62x39 might be my choice for 'practicality' as far as the cartridge, but I'd stick with an 'AK' design firearm due to the type of ammo, cases, and all the feeding issues when trying tapered cases in 'AR' rifles.

On the other hand - 'practicality' seldom governs most firearms purchases - after all it IS a 'hobby' for most of us, so if you get it and play with it and make it work - that will be cool. If it won't work, make a lamp base out of it, or sell it to the next guy who wants to see if he can make it go.

[jdad]

No one wants to see a 7.62x39 upper succeed more than me. I dream of an accurate 7.62x39 with a good scope and premium ammo.I've been reading about it and eagerly following new developments that are supposed to solve the problems.

That being said, in my opinion there are certain engineering issues that are nearly impossible to overcome.

The main one being magazine feeding. Because the magazine well on an AR is straight for several inches, and the tapered x39 requires a constant curve and an angled approach to the feed lips, this issue has yet to be reliably overcome as far as I'm aware. The "Frankenmags" do not have consistent reports even after years of trying to make them work. C products has probably put the most effort in to this as far as I'm aware, and if anyone could make it work, they would be the ones. The cartridge just does not like that straight approach to the feed lips. And even a 10 round SKS magazine has a significant curve/angle to it.

Additionally, the cartridge has a lot of bolt thrust when using steel cases which causes sheared locking lugs. Lugs that are already compromised due to reduced area to accommodate the larger case head.

Years ago the Army requested a rifle that could fire 7.62x39. Knights, LMT and others submitted rifles, the ones I saw all had an angled magwell and used AK or similar mags. Rock River finally built a 7.62x39 rifle in the "AR pattern" but in all completely new dimensions to accommodate the cartridge, a larger bolt/bolt face/locking lugs, and a magwell that uses AK mags.

I still plan to build one, but it will have an improved chamber and .308 barrel vs .311 to shoot what is unofficially called a 30 Grendel (there are other names I cant recall, I think one is .30 GI, the Army shooting team was using it a few years ago), and still shoot the 7.62x39 if needed, though not recommended as the slightly larger bullets cause premature barrel wear.. The straight walled brass case significantly reduces bolt thrust and has a significant increase in powder space giving it 30-30 performance in an AR15 platform.

This all brings us full circle back the the .300BLK. While I take exception to the claims it "equals 7.62x39", It's close enough, it works flawlessly, it uses all the standard AR15 parts except the barrel, it uses standard mags and you can buy ammo for it at almost any Walmart, and it makes a perfect AR pistol or carbine due to excellent performance from short barrels. As much as I wanted to build a x39, I'll be building a .300BLK first.

If you get it, please keep us updated on your progress. I'm eagerly awaiting one that works flawlessly.

I've handled one of these and talked with 2 people that own them. Yes, it's pricey, but built right and accurate.
http://www.cmmginc.com/category_s/1998.htm

Heck, even Hickcock45 likes it. https://www.youtube.com/watch?v=xe48LfRMkt0

[Paladin]

I have one of the old Colt 7.62 x 39 uppers and it works GREAT I swap it around different uppers, it works on full auto, and even worked on full auto with the East German plastic cored training ammo. I use what they call Franken Mags (AK Mags with AR mags tops welded on them). Sorry don't have a photo with me.

[firefuzz]

The main one being magazine feeding. Because the magazine well on an AR is straight for several inches, and the tapered x39 requires a constant curve and an angled approach to the feed lips, this issue has yet to be reliably overcome as far as I'm aware. The "Frankenmags" do not have consistent reports even after years of trying to make them work. C products has probably put the most effort in to this as far as I'm aware, and if anyone could make it work, they would be the ones. The cartridge just does not like that straight approach to the feed lips. And even a 10 round SKS magazine has a significant curve/angle to it.

**********

This all brings us full circle back the the .300BLK. While I take exception to the claims it "equals 7.62x39", It's close enough, it works flawlessly, it uses all the standard AR15 parts except the barrel, it uses standard mags and you can buy ammo for it at almost any Walmart, and it makes a perfect AR pistol or carbine due to excellent performance from short barrels. As much as I wanted to build a x39, I'll be building a .300BLK first.

Here's the major problem and the solution.

Thanks gentlemen for the feedback! I know that the bolt carrier needs to be swapped to accommodate the x39 case. I've read somewhere there have been reports on failed x39 bolts. They just can't take the bolt thrust and some have switched to using 6.5 Grendel bolt carrier.

It's not the "bolt carrier" that's the problem, they are the same. It's the "bolt head" or bolt that's different. Back when I was messing around with the 6.5 Grendel there were some problems with the "bolt" shearing lugs, all smart Grendel shooters had a spare. BTW, the 7.62x39 "bolt" and the 6.5 Grendel are NOT the same. If you're wanting to shoot a .30 cal. bullet out of an AR go with the .300 Blackout. It' not quite as fast with 125gr bullets as the 7.62x39, but out to 300yds. it'd be hard to tell the difference. No mags or bolt problems, just load and shoot.

Rob

[sore shoulder]

I've handled one of these and talked with 2 people that own them. Yes, it's pricey, but built right and accurate.
http://www.cmmginc.com/category_s/1998.htm

Heck, even Hickcock45 likes it. https://www.youtube.com/watch?v=xe48LfRMkt0

Looks like CMMG followed Rock Rivers lead on that. Too bad they probably don't interchange with each other. I like what Grizz said about the 7.62x39's on AR10 platforms, and I'm starting to think that these companies building dedicated 7.62x39 AR pattern rifles are using their .308 bolt carriers and a modified bolt, it only makes sense. If someone built one using the DPMS pattern upper/lower design that used their .308 components it would at least have parts commonality with something. More affordable CNC machines and better design software have made manufacturing a new gun a lot easier. I tend to shy away from proprietary one offs, but I hope they sell a cargo ship full of them. If I were in a collector status, I would have every AR type I could find. Right next to every Marlin I could find, especially take downs.

[hfcable]

here is an article I had read on this subject:

http://www.alloutdoor.com/2014/11/25/ma ... Newsletter

Making An AR-15 in 7.62×39 Work Reliably


Posted 7 days ago in Uncategorized by Major Pandemic with 1 Comment


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Running the 7.62×39 in the AR-15 platform has gotten somewhat of a bad rap. Read through forums and you would think people are a little bi-polar, with one post saying they could never get it to work and the next post noting they bought one off the shelf or built one and never had an issue. Kinda like people who love or hate the 300 Blackout.

Just as I was a fan of the previously cheap-to-shoot 5.45×39 round, I am a fan of the now cheap 7.62×39 round. Prices on that 5.45×39 round shot up a bit after they prevented cheap import surplus rounds, but the 7.62×39 round is still cheap and has been even through the great ammo crisis of the last ten years. I am not kidding. I could actually walk into Cabelas and buy whatever quality I wanted of $6 per 20 boxes of steel cased AK-47 rounds.
•

I have a lot of time behind my AK-47 at this point thanks to 7.62×39 ammo availability. Currently, I am seeing that the venerable 7.62×39 round is still consistently 20%+ less expensive than .223 for plinking rounds. My thought was, “Why not complete a build that could save enough money on the first 2,000 rounds to pay for the entire 7.62×39 AR-15 upper?

Why A 7.62X39 AR-15 Upper?

Some people will ask why you would ever want a 7.62×39 AR-15 upper. Beyond the cost savings, the 7.62×39 is actually a more versatile round in many respects than the 5.56 Nato round and has proven itself as a better deer and hog round by AK-47 hunters. Heck, the 7.62×39 round is basically just an up-powered 30-30 round, which is arguably the most successful deer hunting round in America. The 7.62×39 delivers more energy than the 5.56 Nato/.223 Remington or 300 Blackout out to the 200 yard mark, which is where over 95% of training, plinking, defensive, and hunting shooting is done.

Many will say why not just use the 300 Blackout? Well, from my experience the 300 Blackout round shares many of the same functional reliability problems as the 7.62×39 round running in an AR-15 unless either caliber are well tuned. Yes, yes, I know your 300 BO rifle runs great, but mine needed tuning to run both subsonic and high velocity rounds. Then there’s the fact that the 300 Blackout is still $1.00 a round compared to $0.40 per .223 round and $0.30 per 7.62×39 round. The 300 Blackout has its place, but a working AR-15 7.62×39 upper can deliver more power for less money–you know, if you can get it working.

Major Functioning Issues Of The 7.62X39 In An AR-15

The most significant problem with the AR-15 format running AK-47 ammo has been feeding and functioning. There have been a lot of theories on what exactly is needed to make the round run in the AR-15, but usually it seems to come down to recommendations to start cutting on magazines. I don’t think magazines alone are the culprits. I wanted to see if I could figure it out for you and in the process have some fun with this awesome round.

Every possible problem I could have had with this build, I experienced. Nothing came easy. I placed an order with Delta Team Tactical for a $139 16” 7.62×39 Melonite Barrel with a Carbine length gas system and their complete $139 7.62×39 Phosphate Bolt Carrier Group. Although inexpensive and high quality products, the company could not have screwed up my order more if had been somehow intentional. A month later, I was still working through them sending me the wrong thing–again. Problems were eventually resolved.

I plugged the barrel in a Anderson Manufacturing blemished $40 upper and then used a new Parallax Tactical M-Lock forend. The only real high dollar components on the upper were a Fortis gas block and a Lantac Dragon comp to take the bite out of the heavier recoiling round. A Lucid red dot topped the upper, but it would be months before I was able to really get to using it. For the majority of testing I used my WMD Beast lower.

Getting The 7.62X39 To Work In An AR-15

Once assembled, I ran to the range, excited to function test the build. Testing centered around the inexpensive ammo, with a couple steel cased Wolf and Cabelas Herter’s 7.62×39 rounds using Magpul Pmags and some C-product 6.8 SPC mags, which some had noted would work just fine if used with just a few rounds. They didn’t.

The upper would not feed more than one round at a time and even then seemed to jam the first round on the center of the M4 feed ramp. In many cases it would not even fully extract. When the gun did cycle, it was also short stroking big time and was nowhere near approaching the point where it would lock back on the magazine. Problems? I had problems. Surprisingly the only problem I did not have was detonation. Many have noted that you need a special firing pin, but at least with this standard Mil-Spec lower trigger, there were no detonation issues.

After the first time out, I realized the gun was way, way, way under gassed, with a far too small barrel gas port hole, I also needed a dedicated AR-15 7.62×39 magazine for testing and needed some work on the barrel’s feed ramps.

Many range trips later (test, fail, tinker, and repeat), I had polished the feed ramps to a mirror finish and drilled out the barrel gas port to a huge 1/8 (.125″) size, and suddenly the gun was locking back and at least trying valiantly to pick up the next round in the magazine. Jam city, even with the C-Products dedicated 7.62×39 magazine feeding FMJ, but I really could not fault the magazine. There was more wrong here than magazine issues and what my aggressive feed ramp polish would resolve. That split feed ramp was an issue.

What I found was that most people had figured out the gas port size problem, but feeding was always an issue, and I saw only one company address it completely and that was Bushmaster. Bushmaster offered a 7.62×39 rifle, and from all accounts, it fed and functioned like a dream. The main design difference in these rifles were oversized gas ports and a single large feed ramp, which in essence removed the split between the M4 feedramps to just form one giant ramp.

This made sense because, due to the tapered case of the AK47 round. The round would angle toward the center of the feed ramp when the bolt attempted to pick it up, and guess what is in the middle. Yep, the split in the middle of the M4 feed ramps. So, I whipped out the Dremel and got to grinding away the split. Sure, I took a couple deep breaths before I basically trashed a perfectly good barrel extension, but in my mind it had to be done. It worked perfectly. In fact, now I can feed this upper with pretty much any magazine, but the C-Products dedicated 7.62×39 magazines delivered the best high capacity performance. I would expect any unmodified Stoner and ACS clone 7.62×39 magazines to deliver the same performance.

I have now put twenty full mags through this upper, running on a variety of lower receivers (including the WMD Guns Beast lower) and it has performed outstandingly. In fact, I have had zero functional issues in those 600 rounds other than the very occasional bad round, which is expected with inexpensive ammo.

Why Has Someone Not Figured This Out Before?

Well they have. Bushmaster did, but it was not very popular, leading them to discontinue it. From what I can tell, the single large feed ramp idea died with the discontinued product line. The major problems are that the gas port sizes are almost always too small for the 7.62×39 round and that the split M4 feed ramps only cause jams. If barrel manufacturers delivered a single large feed ramp and 1/8″ gas port hole in the barrel, almost all the issues would be resolved. Add in some dedicated 7.62×39 magazines and you are good to go.

If you have feeding issues, Dremel out the middle of the M4 feed ramp, and it’s likely any feeding issues you are having will disappear. If your bolt is not locking back on the last round, you probably need a larger gas port. In my case I needed to enlarge mine to 1/8″, but you might be able to get away with a smaller port, depending on your build. This process is as simple as removing the gas block and then carefully drilling out the gas port hole to a larger size. I would start smaller and slowly increase the size.

Final Thoughts

Apparently, there are many people who have been able to just buy working 7.62×39 uppers, slam in a dedicated 7.62×39 magazine, and start rocking the round, but the vast majority of folks have issues of some sort. Hopefully, my tips and modifications will allow you to build and enjoy a problem-free AR-15 7.62×39 upper and save some cash in the process as you enjoy a cheaper to shoot AK-47 round. Next up? How about a 7.62×39 AR-15 pistol build.
- See more at: http://www.alloutdoor.com/2014/11/25/ma ... 2537F.dpuf