7.62 in an AR Platform

[Eric P]

Please bear with me on these questions. I have search around and think I have the correct answers. I just want confirmation from the more experienced builders. And please excuse possible errors in part names/terminology.

I have 2 stripped uppers and want to build them to get a better understanding of how the AR works. I already have two .223/5.56 uppers, a 20 inch DPMS bull barrel and a 14.5 inch Yankee Hill (welded flash hider to 16"). So building another .223 would be redundant, so I thought of building them to fire a different caliper and be able to use my existing lowers. 7.62 seems to be an option I see some do. The 7.62x39 and 300 Blackout would be the options. One is cheap and plentiful, the other not so much.

Some questions I have not found clear answers on:

It sounds like standard .223 AR parts can be used for everything other than the barrel, for building a 300 Blackout upper. Is this correct? or is there something I am missing?
.223 magazines would also be used since the cartridge is based on the .223, correct?
Should the weight of the buffer or spring be changed in the stock because of the different energies?


Now if I wanted to go the 7.62x39 route, I would use standard .223 parts other than the barrel and bolt control group.
I have found places to purchase 7.62x39 magazines, but of coarse can't purchase them. I have loaded a few rounds into a .223 pmag and that seems to work, but I can't test it. Other than reduced capacity, any issues in using the .223 pmags?

For either caliper; Should the weight of the buffer and/or spring be changed in the stock because of the different energies?

Also think of building either or both as an SBR with a silencer as I have a 80% lower I want to build also. Any 7.62 model will work as long as the threads are compatible. A 7.62 silencer could be used on .223?

Thank you

[KS63]

I can't comment on the 7.62x39, but I can on the Blackout as I built one. You are correct in that the only change from .223/5.56 is the barrel. The gas system is a little different as far as the gas port size since the Blackout doesn't have as much gas pressure as .223/5.56 to cycle. Magazines are the same, but some .30cal bullet profiles may interfere with the inner rib on some mags. I haven't run into a feeding problem so far with 147gr pulls and lighter projectiles. Same buffer as 5.56 can be used, but most people experiment with buffer weight and adjustable gas blocks.

[ray1970]

My step dad has a factory Colt in 7.62x39. He loves it but quality magazines are definitely required. I can tell you from experience the 5.56 mags won't work with 7.62x39 if you put more than about five or six rounds in them. After that, the taper of the 7.62 round starts causing problems. I'd go 300 Blackout myself. All standard 5.56 parts except the barrel and you can get 30 rounds in a standard 30 round mag. I had one rifle in 300 and it didn't quite cycle reliably with subsonic rounds. If there is a good chance of putting a suppressor on it, I'd definitely go with the 300.

[Eric P]

Thanks.

I think I will start with a 7.62x39 as the 300 Blk ammo is hard to find and pricey.

[KS63]

The thing I hear most about the 7.62x39 in an AR-15 platform are reliability with magazines. If I do my part when choosing projectiles, I never worry about my mags reliability to feed (PMAG). I reload so finding factory ammo isn't a big deal. Reloading the 300Blackout is something that comes with the territory, right now at least. If you're dead set on 7.62x39, Rock River is coming out with their LAR-47 which uses AK mags, but the Lower is a dedicated piece.

[Great-Kazoo]

Buy an AK. Take the money saved on AR mags and the upper, to buy a 300 down the road. The resale, once you tire of it is dismal, to say the least.

[Dave]

I'd say to try the 300 blk, but with ammo price and availability you'd better be reloading if you go that way. If you go 7.62 Soviet, maybe take a trip to NM or WY some day down the road.....

[daknee_k]

I assembled my x39 with a JSE upper and a plastic lower. Took a little finagling to get it to feed consistently but now is a lot of fun for not a lot of money. I bought a bunch of the newer C-products mags and so far am having good luck with them. Either way you go, the 7.62 is a kick to shoot in the AR.