Blademaker

Been thinking of building an AR for a while now, and debating on 5.56mm vs 7.62x39 for a chambering.

I've got a lot of experience with 5.56mm and am not really a big fan of it. On the plus side it's almost no recoil and is accurate at practical distances and there's plenty of surplus ammo out there and it's what the AR was designed for.

7.62x39, a harder hitting, more penetration, I've got tones of ammo already. Not sure how accurate it would be in an AR platform, or even how reliable it would be.

I'm leaning toward 5.56mm just for simplicity and to add yet another caliber to load for.

Also not sure which would be a good manufacture now days.

Any and all thoughts and suggestions welcome.

BTW, I did a search but came up empty.

Thanks.

boomer1983

IMO the 762x39 curved mag looks kinda silly in ar's. the 6.8 is a good compermise if only the ammo wasnt so damned pricey. Id stick with 556 buts to each his own

Depth Afield

Do you plan on shooting paper or flesh? I love my AR in 5.56, simply because it is silly accurate, less expensive to shoot, more capacity, and I have a shotgun and 1911 for defense. Hunting, I use a M700.

SOCOM42

Building an ar in 7.62 brings a whole new meaning to cleaning a rifle. You have in milsurp the most dirtiest and corrosive
7.62x39 ammo going. Will need 3x the cleaning effort. Best be left with their original designs ar=5.56 and 7.62=ak.

CNelson

Why not try 300 blackout? same mags. same lower and upper. heck I believe it even uses the same bolt face.

dont get me wrong. Im not an aac guy by any means. but the cartridge is no longer proprietary. it has gotten saami approved and published. so that means soon there will be more sources for barrels and uppers. not to mention reloading dies and headspace gauges... you name it.

Metonymy

5.56 all the way. Not even a question in my book.

Oxmix

If shooting cheap ammo is what you want, how about 5.45X39. You don't have to worry about reloading as reloading components are almost non existent at this time.

Regards

Ox

Mikey

If your planning on reloading most of your ammo I'd go with a 6.8spc or 6.5 Grendel. It'll be a lot harder hitting and they are designed to run in the ar platform - I have no first hand experience with 7.62x39 ar's but I hear they can be a bit finicky.

As stated earlier 5.45 is a great choice too but it tends to jam up a bit if your using the old Russian surplus ammo - that said I have one and it's a lot of fun and dirt cheap to shoot - if you go with this I highly recommend a piston kit as it'll cut an hour and a half of cleaning and scrubbing down to about twenty minutes.

All that being said, the 556 is still a great choice and with a hot loaded 75 grain bthp it packs a lot of punch.

Blademaker

Thanks, I'm defiantly leaning towards 5.56, but will look into 300 black out, never heard of it before.

Now to figure out what lower to use.

7.62Spark

I built a 5.56 AR-15 last Spring, given that I have heard that some AR-15's have trouble with steel cased ammunition (assuming one is not using the Yugoslavian surplus 7.62X39mm). I decided to use some Wolf .223 in my AR-15, and lo and behold, the casing got stuck in the chamber (I carefully rammed it out with a cleaning rod). The cheap Russian .223 I still have is now strictly for my older Ruger Mini-14, as that gun will digest it without issues.

The 7.62X39mm round is not known for its accuracy, so I decided not to bother feeding such a round through my AR-15 while I was thinking of what to build; I let my AK's and SKS's fire that ammunition.

I have also seen 5.45X39mm uppers, but I believe that all 5.45X39mm ammunition is steel cased, so if some AR-15's have trouble digesting the stuff, I honestly don't see the point of buying a 5.45X39mm upper (I find the cheap 7N6 surplus ammo appealing, but I fire that through a converted Saiga 5.45 rifle, not an AR-15).

I have heard of .300 Blackout, but I am not too familiar with it.

Blademaker

Just got done reading up on 300 blackout, it looks very promising, basically a US version of 7.62x39, but made for the AR, or maybe closer to a 30-30 made for the AR. Got some interesting numbers on it, but it looks expensive if you don't reload.

I'll more than likely go with 5.56mm and be done with it.

Nickoli

I would look into the .300 Blackout, very interesting.

ArmyCPT

Concerning using steel cased ammo - it's not the ammo's fault; rather, it's the .223 chamber in your AR that's holding you back. A 5.56 reamer will fix that for you. I'm not at all familiar with Mini's; however, I think that the Ruger's true 5.56 chamber was a selling point.

The 5.45 uppers (depending on manufacturer) work. I think that S&W even sells one now.

OP, my recommendation is to go with a 5.56 variant. Since you're doing your own build, check out BCM (sold through Bravo Company USA) for a 1/7 or 1/8 barrel, depending on what you'd like this AR to do. They have a multitude of offerings at some very good price points.

Albud3

Believe it or not, the 7.62X39 in an AR platform is decently accurate because of the barrel: tighter tolerances. A friend's AR in 7.62 shot approx. 2.5 - 3.5 moa with mil-surp ammo and around 2 - 2.75 with US ammo. However, the mags are not reliable; all he tried jammed at least once per mag! Plus, they're hard to find and expensive. That's why he sold them.

There is (was?) a manufacturer that sold a modified AR lower that uses AK magazines, but I haven't a clue who it is...maybe someone here knows? I believe it's the same company that sells the modular (can switch between 5.56 and 7.62) lower?

7.62Spark

My rifle is most likely the issue, but I did build it using a 5.56 DPMS upper, so whatever the issue happens to be, I doubt it is the chamber. This rifle fires brass cased, mil-spec 5.56X45mm ammunition without issue and has "DPMS CAL 5.56 1-9" stamped on the barrel.

I see. I was being overly inductive based on the problems my AR-15 has with steel cased ammunition.