I’ve always wondered why a truly well-designed and reliable AR was never created for the 7.62x39mm caliber. Given the following very insightful article discussing the merits of 7.62x39mm, I really have the wonder why it never went mainstream! 6.8 SPC? .300 AAC Blackout? Bah, don’t need 'em. Was 7.62 Soviet all we really needed from the start? Were we blinded by the fact it was “commie” ammo? Just build a reliable AR in 7.62x39mm and you can run cheap steel cased ammo for training, and use top-quality for defense. Some company could make a boat load of money selling these if it could be done.
Thoughts on the article? “Good performance in short-barreled rifles (SBR); the use of modern and heavy projectiles which have near ideal terminal performance; and heavy subsonic loads for suppressed use.” Sound like an ideal AR caliber?
Harrison at AR Performance seems to think otherwise.
So does Karl Lewis with his run of x39 bolts.
PWS seems to be misled with their Diablo 7.5 run in full auto.
I’m especially confused as to why I did this, 2430 rounds ago beginning in May2010.
It is a weaker bolt, but the 6.5 Grendel uses basically the same design and I don’t hear of those breaking much. I have read of a couple, and they were run with handloaded ammo and the receiver’s faces weren’t exactly perfect. Correcting the face of the receiver to be perpendicular with the BCG made a huge difference.
I’ve built 2 x39 ARs, and one upper went to a gentleman in NB. I had 300 rounds through it.
I do run the ASC magazines as much as possible. I also had a Shaw barrel threaded concentric to bore for eventual suppressor use. Shooting through my friend’s YHM SS 762 QD has proved extremely fun.
I made it point to consider a 300blk upper someday, as factory subsonic ammo is available now, and it appears the price will only go down.
But considering I run 70s and 80s yugoslav m67 from AIM for $0.20/rd, I have no reason to consider a 300blk upper yet. I will, sometime after I get my suppressor and decide to run some subsonic loads for shits and giggles.
You may have to polish the feedramps on the upper and barrel extension, but the new ASC mags are worthwhile investments. If you have problems with those, consider Wolff extra power AK47 mag springs and run 25rds in the mag rather than 30.
I wouldn’t mind reading a detailed review of your builds if you’re willing to do one. I’d like to know what parts you used and what kind of reliability you achieved. The only experience I have with Soviet ammo in ARs was a buddy’s 7.62X39 that wouldn’t run and my own 5.45X39 that runs with downloaded mags. The stoppages I remember in the 7.62X39 were all mag related.
Isn’t polishing the aluminum receiver section of the feed ramp is generally frowned upon due to the softness of aluminum without anodizing.
what is the optimal twist rate for that round? I heard that they didnt put the best twist rate in the AK47 because of the existing machinery they still had for the Mosin Nagant which has the same twist rate.
u are absolutely correct. mine is a 16" colt and set up exactly the way u speak of.
runs flawlessly and fun to shoot. thinking of making it my edc car gun.
NAHHHHH but i did consider it.
if its stolen i dont loose much
this is the way it works. mine is all colt except for the model-1 f/p
over 600 rds of very old ak ammo. green box norinco copper stuff. why dont all the ney sayers actually shoot 1 before shitting on it. F.N.V. goes a long way here, or anywhere.
It is simply not possible to put a curved magazine into a straight magwell. After not having luck with that, I bought a Special Weapons lower that took AK magazines. I still have it, but stripped it down after I broke two bolts. Oh yeah, in order for the mags to fit, you have to mill the bottom of the BCG to clear the mag feed lips.
It is ok for casual shooters, but it is outside of normal engineering practice so you can’t make a production run of guns and expect them all to work.
My 10.5" gun uses a LMT upper and lower which were cerakoted in 2009.
The barrel is a 10.5" Shaw 10 twist with a carbine gas port at .094 and it runs on 1970s and 80s vintage Yugoslav M67. I use an H2 buffer and LMT carbine spring in this weapon. Originally the barrel was 16" but a friend of mine who works for a local AR MFG shortened and threaded it for a QD suppressor mount. The times I’ve shot it suppressed have been enlightening. I hope to have my silencer by Memorial Weekend 2012.
Polishing the aluminum and matching the feedramps has not been a detriment to the upper receiver itself. This was done at approximately 300 rounds and has had over 2100 rounds sent downrange since then. I do not see any noticeable wear whatsoever. Most of the rounds since then have been corrosive with a handful of zinc plated MFS sent through it because someone at the range wanted to try it and they had that available to them after I was done. I wanted to see how it ran with that ammunition also in the event I cannot find more M67. There were no stuck cases or failure to hold open on the last round.
The BCG is LMT, with a Model 1 Sales firing pin. Other shooters of this caliber in ARs have commented it fixes much of the FTFire associated with east european ammunition. This was case for me.
I run ASC and CProducts magazines and have had wonderful success with the ASC magazines. It shows they’re willing to produce something good and after running 5 of them I am on the waiting list at AIM to purchase more when my email notifies me they’re in stock. Some of the CP magazines I have needed extra power mag springs designed for the AK 47 from Wolff. When a magazines does not perform like I expect it to I order more springs. Retrofitted magazine springs have shown the deficiency of the older springs which, IMHO, were not long enough to support the weight of 25 rounds of 123gr loaded ammunition. When I install a new mag spring I paint the body of the magazine with a number so I know which ones I’ve done.
One of the biggest things I consider beneficial to running this caliber in the AR platform is that you have ergonomics, choices of stocks, forearms, VFGs, optics, and quality parts. LMT has made some excellent bolts, as has Harrison at AR Performance. His barrels and bolts are quality pieces—there is no denying that—and the .700 profile Scout is something many barrel makers should consider due to the wall thickness being similar to a pencil profile 5.56 barrel. If ARP had x39 carbine barrels and bolts at the time I was building this upper I’d have gone in that direction but they’re midlength and I wanted a 10.5" upper. You need a carbine or pistol length gas system to run that length barrel.
I’m extremely happy with mine since building it.
Regarding the 16" carbine upper I built for myself—I used a Shaw barrel and ran a Troy MRF-R. The FSBs on both uppers were shaved and profiled to fit inside forearms. It was a backup gun to my 6.5 Grendel and it gave me no issues either. I only ran 10rd magazines in it and it had a SOPMOD stock TNW lower receiver with a polished trigger and JP reduced power trigger spring kit. The magazines ran very well, and it was a about a 4moa gun using the Leupold 4-12x40 I had for it. The BCG was an auto carrier and bolt from JSE Surplus. I decided to sell it as it saw very little use.
FWIW, that LMT upper has seen several different freefloats on it. Each has had it’s own set of strengths and weaknesses but I’d be a willing participant of Daniel Defense’s testing if they came out with a specific 10" version of their Modular Float Rail. I machined the 12" model down to work on this gun and it has performed perfectly. It hasn’t come loose, and through high volumes of fire and drills I am extremely pleased with it.
I put together an M-4 style civilian legal carbine that shot the 7.62 X 39 round. Basically I used an upper from Model “1”, a lower from Rock River Arms and magazines from C-Products. I used it in a police car and tested it on some ranges where I live. I loved the assembly and it shot great. The round had really good penetration that the .223 caliber ammo didn’t have. As is common with ARs and M-4s, the worst problem area is almost always the magazines. The sides of the magazines are not as strong as they should be so they bulge outwards about half way down. It is not uncommon for magazines to end up with a double stack jam (2 rounds sitting side-by-side half way down the magazine) that keeps the rifle from working. Because of a series of jams, I ended up retiring the assembly and magazines. I would also like to see a good M-4 type carbine using the 7.62 X 39 ammo come to life with really strong magazines sort of like what most AKs use. Now don’t take me wrong. C-Products did make a good product so I don’t blame them for the problems I encountered. I tend to believe that the bigger, heavier 7.62 X 39 ammo creates problems associated with its design, weight and diameter characteristics that are not easily overcome. That’s probably why the magazines used by the AKs are so heavy and thick and not at all like our magazines.
KAC made what looks to be amazing weapon with the SR-47 back in 2001 or 2002. I wish they would license the design to a commercial entity. An AR that uses AK mags while retaining the AR’s manual of arms (other than magazine changes) would be very, very cool. Anyone know if the AR-47 by Michael Machine works?
I’d love to hear more about the SR-47 from III or Kevin B
The issue with 7.62x39mm comes down to the magazine well and how it interacts with magazines. You have a straight magazine well, and a heavily tapered cartridge… while you might be able to get by, it isn’t an ideal scenario.
The other issue is that 7.62x39mm is an inferior cartridge compared to 6.8SPC, 6.5 Grendel, 5.56NATO, etc. You are sacrificing having a sound design as far as the magazine goes, and not really gaining anything.
7.62x39mm will never be a winner in the AR15 platform. To do it “right” would require a complete redesign of the lower receiver. In the end, it will be so expensive that it makes more sense to either get something Kalashnikov-based, or just get an AR in 6.8SPC or 6.5Grendel.
Reloaded it still won’t be as cheap. Comparison of the x39 to 6.5 Grendel is hardly fair as 6.5 is supersonic to 1k yards in the same weight with a 16" barrel. This isn’t the purpose of the round. And the cheapest you’ll reload it for is still 2x the price. If you want to burn through 6.5 at that rate go on and do it. I don’t shoot my 6.5 that heavily. It has a different purpose.
so you either go thru major gyrations and reliability issues plus some serious $$ to get the Russian round to fire in an AR or shoot the 300 for $ more. Looks like a toss up to me.
300 BLK is cheaper than 7.62x39mm if you go by US-made brassed-cased ammo. It is only when you start to talk about surplus or steel imported ammo where AK ammo is cheaper.
AK ammo has special firing pin requirements, and you would want to put in an extra-power hammer spring - and then you may not want to use that lower with 5.56mm anymore. Also you cannot make the magazines work no matter who says otherwise. I mean you can get one to work on a video, but you cannot mass produce working guns because the curve just does not fit the magwell.
I have a Special Weapons dedicated lower that takes AK mags, but I had to mill the bottom of the bolt carrier to clear the magazine feed lips. It is sort of a poor-man’s SR-47. It worked ok, but I broke two bolts within 500 rounds, and so gave up. At the time, I was going out of my way to not do anything 300 Whisper(R) related, because I did not believe in wildcats, and expensive ammo ($45 a box) and expensive brass ($1 each). Now that 300 BLK is SAAMI, that is the lowest cost decent solution. $12.99 MSRP ammo and reformed brass for as little as 10 cents a case.
Fiocchi is about $10 for reloadable brass x39. I picked some up at Sportsmans Warehouse for less than that last year also.
You are correct on the firing pin requirement, in most cases. AR Performance shooters have noted that a specific firing pin is not required on their guns as they’re running a stock firing pin. I have no problems believing that Harrison knows what he is doing with these weapons. And shooters like his products. If he’d make carbine length barrels I’d build another SBR upper immediately. I also do not run an extra power hammer spring. My gun simply does not need it.
Regarding magazines working—I’m not sure why mine are operating or why several other people I’ve researched are having success here. CPRoducts magazines are not the best in the world and there was a regime change in Connecticut due to it. ASC is producing better magazines now, and none have given me issue. If they were, a full auto run of the Diablo would be impossible. I’m not the only sucess story here with running it. I mean I didn’t order specific magazines from ASC through AIM to get lucky. I didn’t tell them to give me better springs. I just ordered them and they work.
I’ll also consider myself ridiculously lucky that I’ve run a 10.5" upper for over 2430 rounds now on the original bolt. You may want consider other people’s successes before saying that the only 30 caliber AR solution is 300blk. I’m sorry your gun didn’t last more than 500 rounds. I will happily consider shooting 300blk when I build my own upper for it. Until then, I’m running a 10.5" weapon with 123gr pills at 2100fps for $0.20/rd, and I have thousands of them.
You don’t even have to post, but go read on TOS about how many x39 shooters there are having success. Just look under variants. I’d link all of them for you but I don’t have that kind of time right now. Where 300BLK wins, is loaded subsonic ammo, of which I am interested. Speaking of 10c brass cases, I’d still have to load them up with 30c worth of primer, projectile, and powder. As I mentioned once before, when 300blk gets to 30c a round for factory ammo I will throw my x39 barrels out the window. I hope it does, because I like PMags
