AR-15 parts (7.62x39mm)

**lexnaturalis** · January 14th, 2010, 11:22 AM

I have a few questions (and might have more as the thread progresses). I'm currently pricing and speccing out parts to build my first AR-15. I discovered I can get it in the standard 5.56/.223 caliber as well as 7.62x39mm. I already own an SKS and have reloading equipment for 7.62 so this is good news for me.

I'd like to ultimately build an upper for both. It is my assumption (based upon my research) that I can use the same lower for both calibers. Is that correct?

Also, when speccing out individual parts for the upper I see that I can buy a bolt assembly for different calibers. That leads to the second question. What do I need to do to convert from one caliber to another?

If I build it in 5.56, what do I need to change to convert it to 7.62? Do I just need a new barrel and bolt assembly? Or is the upper receiver itself different?

For right now I'd like to buy as few parts as possible that let me fire both 5.56 and 7.62. If I have to buy a completely new upper for 7.62 that's fine, but I'd like to know that ahead of time.

Thanks!

**IronButt** · January 14th, 2010, 12:01 PM

I'm just speculating, but I would think that the larger diameter of the 7.62X39 cartridge would require a complete upper. Cartridge length is roughly the same, so the lowers might be interchangeable.

I'm sure someone's done this & will be along shortly.

**lexnaturalis** · January 14th, 2010, 01:04 PM

Originally Posted by IronButt

I'm just speculating, but I would think that the larger diameter of the 7.62X39 cartridge would require a complete upper.

That's my speculation as well. My problem is that I haven't found anywhere that sells an upper specifically for 7.62x39. I've seen lots of upper assemblies for that caliber, so that's why I thought maybe it was just the bolt assembly that was different.

Or my Google-fu is weak and there really are specific uppers and I can't find them. That's a distinct possibility

**SlimShady** · January 14th, 2010, 02:25 PM

Originally Posted by lexnaturalis

That's my speculation as well. My problem is that I haven't found anywhere that sells an upper specifically for 7.62x39. I've seen lots of upper assemblies for that caliber, so that's why I thought maybe it was just the bolt assembly that was different.

Or my Google-fu is weak and there really are specific uppers and I can't find them. That's a distinct possibility

There're a few companies that make complete 7.62 X 39 rifles so finding just an upper should be possible. Check out Stag, Armalite and maybe some of the other shops like the ones I can't freakin' think of right now. ARRGGHH!!!

There's a shop in Dallas Tx that sells a ton of AR uppers and lower as well as complete guns, advertise on several boards and in several magazines........someone will be along to name them sooner or later.

**1832** · January 14th, 2010, 03:00 PM

Check out Model 1 Sales for the 7.62x39 Upper. Some bolt groups have a problem igniting the hard Russian primers. You can play with firing pin protrusion, heavier hammer springs, etc., but I found the easiest solution was to order the "Enhanced" 7.62x39 Bolt from MGI. I've run one in my Model 1 Upper for nearly two years now with no failure to fire with any type of steel cased ammo.

P.S. Brown Bear HP seems to be the most accurate out of my upper.

**lexnaturalis** · January 14th, 2010, 03:04 PM

The only reason I'd really want an upper for 7.62 is that I reload that already and have plenty of bullets/cases/primers on hand. So for now, anyway, the steel cases and Russian primers wouldn't be a problem.

So I do have to buy an upper specifically for the caliber though? Thanks! At least now I know.

If I ever decide to shoot surplus ammo I'll look into that bolt too.