AR in x39?

[Atlantis]

So I want to keep training, and I don't want to switch platforms to AK, and I don't want to burn through my stockpile nor do I want to pay the price that 5.56 is going for.

Naturally, I decided to build a frankengun, and will be building an AR Pistol in 7.62x39.

I found a nice build kit for $489, seems to be pro2a anti tyranny in terms of shipping, and the only complaint I have is the crappy pistol tube brace that will become something sensible like an SBA3/4 brace.

Specs on the build kit

• Made in the USA
• Mil-Spec Lower Parts Kit
• Mil-Spec 7075 T6 Upper Receiver with Dust Cover and Forward Assist
• 10.5" 1:10 Twist 4150 Barrel with Black Nitride Finish
• Chambered in 7.62X39
• Carbine Length Gas System
• .750 Low Profile Gas Block
• 10" Free Float M-LOK Hand Guard
• Bolt Carrier Group
• Charging Handle

STONER 10rd mags for compliance. I believe there are a 30 round variety for when I live in a free state as well.

Questions:

Anyone ran a setup like this? Do you like it?
Would an A2 flash hider make it not "terrible" in terms of blast/flash? My 10.5 5.56 is pretty tolerable with an A2?
Are there any better suggestions than a MA-Lock for complying with the fixed mag requirements of MA? Something that meets the requirements but is a little easier to reload than breaking the action with a takedown pin every 10 rounds?
Mag issues? Suggestions?
What about buffer and spring weights? Any advice? Thinking maybe I want a heavy buffer?

 

[drgrant]

Run away. Run far away, forget you ever thought it was a good idea.... those guns are dumpster fires and always will be....

 

[Atlantis]

Run away. Run far away, forget you ever thought it was a good idea.... those guns are dumpster fires and always will be....

I suppose this is a bad time to mention that everyone I just listed is paid for and allegedly en-route? Along with a couple cases of non-magnetic steel case ammo?

Best I can tell the number one complaint is that the straight wall of an AR magwell doesn't play nice with the tapered x39 cases.

Otherwise it seems like the lug failure issue is not super common, and the under/overgassing can be addressed with some tuning.

 

[drgrant]

You'll be dumping it soon. These guns were never meant for this cartridge. I've not met a single person that kept a 762 x39 AR.... ever.

 

[Atlantis]

You'll be dumping it soon. These guns were never meant for this cartridge. I've not met a single person that kept a 762 x39 AR.... ever.

Correct me if I'm wrong here, but isn't the original design of the AR-15 stemming from the AR-10? Which was designed for 7.62x51? Again, correct me if I'm wrong here, but I thought that the 7.62x51 and 7.62x39 were quite similar, more so than 5.56 is to x39?

I mean your point stands, the AR-15 is clearly designed for 5.56. But also for a 20" barrel.

I didn't mention it in the OP, but my other design criteria here is I am going for a CQC type weapon, with a much shorter barrel. I have a scoped AR build for longer range work. I don't love the ballistics of the 5.56 in a 10.5" though, so the idea is to replace my 10.5" 5.56 with a better caliber. I would have gone .300BO but that is not logical given the current ammo situation.

So for something intended for short range, x39 seems to be a better caliber in a 10.5" barrel. So long as I can make it feed properly, seems like a win win? I can retain proficiency with a single platform, and not spend an arm and a leg on ammo.

 

[jpm]

I run a 16" x38 AR and it works just fine. The biggest problem I ran into was with the hammer spring being not strong enough to set off the military primers in some ammo (like Golden Tiger). Wolf and Tula were fine though. Pretty good accuracy too. I run a standard A2 flash hider on it (30 cal size of course) and don't see any flash. But its 16" barrel too so I'd expect some flash out of a shortie.

The mag problem is not with the straight wall mags that you mentioned its with the curved ones. I found a couple of pre-ban 30rd x39 mags and neither one would feed properly with more than 6 or 7 rounds in it. The AR Stoner 10 round mags that Midway sells for 15 bucks work great. VERY strong springs in them so they'll need some break in before you get that 10th round in there easily.

 

[knoxy]

Run away. Run far away, forget you ever thought it was a good idea.... those guns are dumpster fires and always will be....

LOL, we know you hate these!

I've got to say I love my AR in 7.62×39. Been 100% awesome.

But it's just a PSA and you can't have one

 

[SKumar]

Yeah I looked into those as well. Stay away from AR15s chambered in x39, magazine feed issues abound. However, I recently picked up an AR that takes AK magazines, which solved my concerns. Very hard for me to obtain, but so far shoots like a dream.

 

[Atlantis]

I run a 16" x38 AR and it works just fine. The biggest problem I ran into was with the hammer spring being not strong enough to set off the military primers in some ammo (like Golden Tiger). Wolf and Tula were fine though. Pretty good accuracy too. I run a standard A2 flash hider on it (30 cal size of course) and don't see any flash. But its 16" barrel too so I'd expect some flash out of a shortie.

The mag problem is not with the straight wall mags that you mentioned its with the curved ones. I found a couple of pre-ban 30rd x39 mags and neither one would feed properly with more than 6 or 7 rounds in it. The AR Stoner 10 round mags that Midway sells for 15 bucks work great. VERY strong springs in them so they'll need some break in before you get that 10th round in there easily.

Good to know, I have heard similar issues with the hammer spring but figured I'd wait to see how it works out of the box first. I ordered 2000 Red Arm Standard which I think is just Tula.

It's interesting that its only apparent in the 30's not the 10's though. Maybe a different follower? Any experience with the AR Stoner 30's, new ones? I'm hoping those would work reliably in a free state.

What gas system are you using and buffer weights? I have a carbine length gas system, standard carbine spring and buffer, and I ordered an H buffer as well.

I've read alot of people have issues with the gas port size and end up drilling it out. Again, I want to wait and see how mine runs out of the box, but curious if you had to address this?

LOL, we know you hate these!

I've got to say I love my AR in 7.62×39. Been 100% awesome.

But it's just a PSA and you can't have one
View attachment 374897

Lol if they had anything in stock they would be my first stop. All of my AR builds so far have been PSA, can't speak highly enough of them for the price point.

Yeah I looked into those as well. Stay away from AR15s chambered in x39, magazine feed issues abound. However, I recently picked up an AR that takes AK magazines, which solved my concerns. Very hard for me to obtain, but so far shoots like a dream.
View attachment 374894

That would be a dream, but harder to obtain that it is for me to build. Everything I've read says the split feed ramps can cause an issue, but that's nothing a dremel/file can't fix if you want to copy bushmaster and make one big ramp

 

[Picton]

Get an AK.

It'll make you a better-rounded shooter. And they're cooler.

 

[Rocky Mosasaurus]

^^^I have also heard (Demo Ranch) that ARs which feed AK mags seem to be the go-to move.

 

[JRT]

You'll be dumping it soon. These guns were never meant for this cartridge. I've not met a single person that kept a 762 x39 AR.... ever.

I'm not sure if you are putting the Sig 556R in this group, my 556R is super reliable. Yes, I sent the original dumpster fire of a rifle back to Sig and they sent me a new rifle, the new one has been flawless. The old style wasn't so much an issue with 7.62 x 39 as it was just shitty QA.

 

[drgrant]

I'm not sure if you are putting the Sig 556R in this group, my 556R is super reliable. Yes, I sent the original dumpster fire of a rifle back to Sig and they sent me a new rifle, the new one has been flawless. The old style wasn't so much an issue with 7.62 x 39 as it was just shitty QA.

Different gun totally, at least the 556R is piston driven and takes AK mags. Most of the rest of these guns are some frankengun where some guy thought it would be cute to make a 762 x 39 AR upper, and weirdo mags that somehow sorta kinda work with it. "Sorta Kinda" being the operative terms.

 

[drgrant]

I run a 16" x38 AR and it works just fine. The biggest problem I ran into was with the hammer spring being not strong enough to set off the military primers in some ammo (like Golden Tiger). Wolf and Tula were fine though. Pretty good accuracy too. I run a standard A2 flash hider on it (30 cal size of course) and don't see any flash. But its 16" barrel too so I'd expect some flash out of a shortie.

Any gun that can't run GT is broken, in my book. Although depending on circumstances that might be a fixable problem.

 

[Atlantis]

Different gun totally, at least the 556R is piston driven and takes AK mags. Most of the rest of these guns are some frankengun where some guy thought it would be cute to make a 762 x 39 AR upper, and weirdo mags that somehow sorta kinda work with it. "Sorta Kinda" being the operative terms.

Well as long as its in mass, I am only allowed to run a 10rd fixed mag. So as long as it runs 100% in that configuration, I am just upgrading my existing 10.5" from 5.56 to x39. If it can never handle a standard cap mag, then what you are saying starts to carry more weight with me. But where I live now, in this crappy state, it's a money saver for me, plus a better caliber out of a short barrel.

 

[SKumar]

Sig556R, M&M M10x, PTR32. All take AK magazines and are likely better options than an x39 AR15.

 

[Atlantis]

Sig556R, M&M M10x, PTR32. All take AK magazines and are likely better options than an x39 AR15.

If you have a lead on how I can legally purchase any of those and keep total cost ~$600-700, I am ALL ears haha

 

[drgrant]

Well as long as its in mass, I am only allowed to run a 10rd fixed mag. So as long as it runs 100% in that configuration, I am just upgrading my existing 10.5" from 5.56 to x39. If it can never handle a standard cap mag, then what you are saying starts to carry more weight with me. But where I live now, in this crappy state, it's a money saver for me, plus a better caliber out of a short barrel.

Lol 10rd fix mag? why even bother, unless we're talking one of those deals where you only run it out of state and cripple it when it comes back in, etc.

I would never even fire a single shot out of a 10 rd fixed mag gun. It would be "for compliance only" when it's not in use.

Basing gun purchasing decisions around shitty laws is typically harmful to ones psyche. I'd rather not have it at all than deal with that, even holding the thing is like being kicked in the
balls every time. It's like a pinned collapsible. That's even more gay than a fixed stock.

 

[greencobra]

I've not met a single person that kept a 762 x39 AR.... ever.

ahhh...we've not met but you yell at me on ocassion. i'm raising my hand slowly...me, i have two 7.62x39 ars. i'm sorry to go against the grain again. i'll do better.

@Atlantis i run asc mags, don't know why, maybe i live a charmed life, but they work just fine.

again, i apologize to the oracles and gurus.

 

[drgrant]

ahhh...we've not met but you yell at me on ocassion. i'm raising my hand slowly...me, i have two 7.62x39 ars. i'm sorry to go against the grain again. i'll do better.

@Atlantis i run asc mags, don't know why, maybe i live a charmed life, but they work just fine.

again, i apologize to the oracles and gurus.

Hey if you like it, and it works, then you are THAT GUY. I'm glad yours works.

 

[Atlantis]

Lol 10rd fix mag? why even bother, unless we're talking one of those deals where you only run it out of state and cripple it when it comes back in, etc.

I would never even fire a single shot out of a 10 rd fixed mag gun. It would be "for compliance only" when it's not in use.

Basing gun purchasing decisions around shitty laws is typically harmful to ones psyche. I'd rather not have it at all than deal with that, even holding the thing is like being kicked in the
balls every time. It's like a pinned collapsible. That's even more gay than a fixed stock.

I hear ya, but if SHTF its pretty easy to reconfigure lowers and uppers, and not to hard to drill out what needs drilling to unfck the lowers that have been bastardized.

I am less and less concerned with compliance as the days go on, but I have plenty to lose right now by being stubborn.

 

[greencobra]

Hey if you like it, and it works, then you are THAT GUY. I'm glad yours works.

friends then?

 

[Picton]

Basing gun purchasing decisions around shitty laws is typically harmful to ones psyche. I'd rather not have it at all than deal with that, even holding the thing is like being kicked in the
balls every time. It's like a pinned collapsible. That's even more gay than a fixed stock.

I hear ya, but if SHTF its pretty easy to reconfigure lowers and uppers, and not to hard to drill out what needs drilling to unfck the lowers that have been bastardized.

I am less and less concerned with compliance as the days go on, but I have plenty to lose right now by being stubborn.

Many of us arrive at a certain point in our Massachusetts gun-ownership journey where we understand that it's simply worth saving up a few hundred extra bucks, then buying preban. It sucks that we need to do this, but the headaches it removes are worth the money. YMMV.

 

[Deleted member 67409]

Correct me if I'm wrong here, but isn't the original design of the AR-15 stemming from the AR-10? Which was designed for 7.62x51? Again, correct me if I'm wrong here, but I thought that the 7.62x51 and 7.62x39 were quite similar, more so than 5.56 is to x39?

I own rifles in both 7.62x51 and 7.62x39. The two cartridges are not similar. They're similar only vaguely in bore diameter. Frankfort Arsenal derived 7.62x51, aka 7.62 NATO, from .300 Savage. The .300 Savage is a lever action caliber designed to work in the Savage 99 rifle as a "close enough" substitute for .30-06 in the 99's shorter action. Frankfort tinkered with .300 Savage during the post-WW2 1940s, and by the 1950s, .308 Winchester and then 7.62 NATO emerged as a replacement for .30-06 that maintained the ballistic capability of .30-06 in standard military ball and armor piercing loads.

The Soviets developed 7.62x39 to work in their nascent intermediate cartridge project rifles, such as the SKS and AK-47. 7.62x39 was intended from the get-go to be a mild-recoiling, full-auto friendly cartridge effective within 300-400 meters in light, handy carbines like the SKS and AK-47. 7.62x39 was never intended to fully replace 7.62x54r, which kept on as a sniper's/designated marksman's/machine gun cartridge to this day, but rather to replace 7.62x54r and 7.62x25 for most front and rear echelon troops that otherwise would've had a Mosin, PPSh-41, or PPS-43.

The two cartridges have different bore diameters: 7.62 NATO is 0.308", 7.62x39 is 0.311". The pressures are off by about 9,000: per Wikipedia (check a handloading manual), 7.62 NATO has about 60,191 psi of max pressure, 7.62x39 has about 51,490 psi of max pressure. 7.62x39 is more tapered of a case than 7.62 NATO. The cases are obviously 12mm different. 7.62x39 usually is made of steel cases; originally, 7.62 NATO was exclusively brass cases. 7.62 NATO has more recoil and ballistic energy than 7.62x39. The magazines in both 7.62 NATO and 7.62x39 rifles are quite different; simply put, it would be very hard for an informed gun owner to fail to notice the differences between a FAL or M14 or G3 mag and an AK-47 or Yugo M70 mag.

I spent this afternoon shooting 7.62 NATO and 7.62x39 and I can tell you that the cartridges are not similar. Eugene Stoner wouldn't have had access to 7.62x39 in all likelihood when he designed the AR-10 and AR-15; he may have been aware of it, but he wouldn't have likely had access to 7.62x39. He wasn't considering 7.62x39 when he designed either the AR-10 or AR-15. Similarly, the designers of 7.62x39 likely were not examining .300 Savage during WW2 when developing 7.62x39.

7.62x39 and 5.56x45 are more similar to each other than you think. Both are intended to be effective within 400 meters, rather than beyond that. Both have similarly low recoil. But the cases are much different; again, I was looking at 7.62x39 and 5.56x45 cases this afternoon and 5.56 is a straighter, thinner case with a thinner rim. 7.62x39 is more tapered, fatter, and shorter.

 

[Atlantis]

I own rifles in both 7.62x51 and 7.62x39. The two cartridges are not similar. They're similar only vaguely in bore diameter. Frankfort Arsenal derived 7.62x51, aka 7.62 NATO, from .300 Savage. The .300 Savage is a lever action caliber designed to work in the Savage 99 rifle as a "close enough" substitute for .30-06 in the 99's shorter action. Frankfort tinkered with .300 Savage during the post-WW2 1940s, and by the 1950s, .308 Winchester and then 7.62 NATO emerged as a replacement for .30-06 that maintained the ballistic capability of .30-06 in standard military ball and armor piercing loads.

The Soviets developed 7.62x39 to work in their nascent intermediate cartridge project rifles, such as the SKS and AK-47. 7.62x39 was intended from the get-go to be a mild-recoiling, full-auto friendly cartridge effective within 300-400 meters in light, handy carbines like the SKS and AK-47. 7.62x39 was never intended to fully replace 7.62x54r, which kept on as a sniper's/designated marksman's/machine gun cartridge to this day, but rather to replace 7.62x54r and 7.62x25 for most front and rear echelon troops that otherwise would've had a Mosin, PPSh-41, or PPS-43.

The two cartridges have different bore diameters: 7.62 NATO is 0.308", 7.62x39 is 0.311". The pressures are off by about 9,000: per Wikipedia (check a handloading manual), 7.62 NATO has about 60,191 psi of max pressure, 7.62x39 has about 51,490 psi of max pressure. 7.62x39 is more tapered of a case than 7.62 NATO. The cases are obviously 12mm different. 7.62x39 usually is made of steel cases; originally, 7.62 NATO was exclusively brass cases. 7.62 NATO has more recoil and ballistic energy than 7.62x39. The magazines in both 7.62 NATO and 7.62x39 rifles are quite different; simply put, it would be very hard for an informed gun owner to fail to notice the differences between a FAL or M14 or G3 mag and an AK-47 or Yugo M70 mag.

I spent this afternoon shooting 7.62 NATO and 7.62x39 and I can tell you that the cartridges are not similar. Eugene Stoner wouldn't have had access to 7.62x39 in all likelihood when he designed the AR-10 and AR-15; he may have been aware of it, but he wouldn't have likely had access to 7.62x39. He wasn't considering 7.62x39 when he designed either the AR-10 or AR-15. Similarly, the designers of 7.62x39 likely were not examining .300 Savage during WW2 when developing 7.62x39.

7.62x39 and 5.56x45 are more similar to each other than you think. Both are intended to be effective within 400 meters, rather than beyond that. Both have similarly low recoil. But the cases are much different; again, I was looking at 7.62x39 and 5.56x45 cases this afternoon and 5.56 is a straighter, thinner case with a thinner rim. 7.62x39 is more tapered, fatter, and shorter.

I asked to be corrected and boy was I! Thank you for the detailed write up. Noted!

 

[SKumar]

If you have a lead on how I can legally purchase any of those and keep total cost ~$600-700, I am ALL ears haha

No way will you find them that low. Expect $1-1.5k minimum, plus finding the gun, plus shipping, plus finding an FFL willing to transfer, plus transfer fee.

If you want to shoot x39 on the cheap, take a look at a military surplus SKS. They have an internal magazine, shoots wonderfully, milled receiver, tilting-bolt action, wood stock.

 

[Deleted member 67409]

I asked to be corrected and boy was I! Thank you for the detailed write up. Noted!

No way will you find them that low. Expect $1-1.5k minimum, plus finding the gun, plus shipping, plus finding an FFL willing to transfer, plus transfer fee.

If you want to shoot x39 on the cheap, take a look at a military surplus SKS. They have an internal magazine, shoots wonderfully, milled receiver, tilting-bolt action, wood stock.

Honestly, the real solution here is to get a .300 Blackout upper. The .300BLK solves all of the "issues" of 7.62x39 in an AR and uses 0.308" bullets rather than 0.311". There's the added benefit of suppressor-friendliness for those in can-legal states, which is basically everywhere except Mass, RI, and a couple other states. .300BLK fits in standard 5.56 AR mags.

I realize that .300BLK is unobtanium right now, but anyone who shoots a substantial volume of the cartridge usually has a handloading setup where they'll trim and re-shape 5.56 cases into .300BLK cases. So, if someone can handload 5.56, they can also handload .300BLK.

That'll give OP what he wants - a new caliber in the AR platform that he could shoot when he doesn't want to cut into a stash of 5.56.

 

[Atlantis]

Honestly, the real solution here is to get a .300 Blackout upper. The .300BLK solves all of the "issues" of 7.62x39 in an AR and uses 0.308" bullets rather than 0.311". There's the added benefit of suppressor-friendliness for those in can-legal states, which is basically everywhere except Mass, RI, and a couple other states. .300BLK fits in standard 5.56 AR mags.

I realize that .300BLK is unobtanium right now, but anyone who shoots a substantial volume of the cartridge usually has a handloading setup where they'll trim and re-shape 5.56 cases into .300BLK cases. So, if someone can handload 5.56, they can also handload .300BLK.

That'll give OP what he wants - a new caliber in the AR platform that he could shoot when he doesn't want to cut into a stash of 5.56.

Long term, that is exactly what I intend to do. At this point in my life I just don't have the bandwidth to get into reloading. I'd like to be able to keep paying TSUSA to feed my builds for the time being. So despite the (much appreciated) noted concerns, I will be pressing on with this build. I have a properly set expectation that this setup may require some gunsmithing to become reliable.
Also, in reference to @SKumar, I have my eye out for an SKS at typical pricing. I realize the prices may never go back to normal, but it's definitely on my list.

Keep in mind, I have a 10.5" fixed mag 5.56 build that this is intended to REPLACE. So the fixed mag nonsense is already a part of my life, not some new burden. Think of this more as a caliber upgrade for a shorter barrel with the added benefit of better ammo availability. If I can be confident that it runs reliably with 10rd mags, I can unfck the fixed mag issues pretty quick in SHTF scenario.

 

[PappyM3]

I asked to be corrected and boy was I! Thank you for the detailed write up. Noted!

Also, the AR-10/SR-25/AR308 are COMPLETELY different firearms than AR-15 variants. Just about everything on an AR10 is bigger, to include the lower(magwell bigger too) and upper receivers

 

[jpm]

Any gun that can't run GT is broken, in my book. Although depending on circumstances that might be a fixable problem.

lol well it was simply a matter of swapping in a stronger hammer spring and problem was instantly solved. Or I could run every round through twice and the primers would light after a second strike.