A friend of mine has been on a quest to build a heavy hitting AR rifle without the AR10 price tag. First, He bought a new DPMS lower (.223 stamped on it). Today he brought over a "pre-ban" DPMS upper and five magazines. We assembled the rifle and went to the range. The first glitch we had were failures to feed. We deducted this to cheap magazines eventhough it did it with all of them(plastic 10 rounders and metal 20+ rounders). The biggest problem we had was the inability of the firing pin to strike some of the primers hard enough to ignite them.

Is there a difference in lowers, ie .223 lower vs. 762x39 lower?

He claims to have done research on this and stated the 223 lower should work fine. What are we missing in this senario?

Thanks in advance,
Joe

7.62x39 build can be tricky. First of all, there is no such thing as a 7.62x39 specific lower. They all use a standard .223 spec type lower. Many problems can be had with these builds. First of all the gas ports may need to be enlarged depending on ammo. A carbine short system tube seems to work better. Another problems seems to be reliable mags. AK mags curve for a reason due to round design of the 7.62x39 cartridge. With that said, mags are a trial and error with no real sure proof mag that I know of. I have used a MWG and a USA mag steel ten rounder with good results. The next facet of these rifles is with the exception of Colt IIRC, most bolt faces are just a opened up .223 bolt that leaves a thin weak extactor and bolt face. I suspect this also factors in with the firing pin protrusion.
While this may not give you a fix for your particular rifle, these are the areas I would look at in trouble shooting.

Hootbro

Quoted: 7.62x39 build can be tricky. First of all, there is no such thing as a 7.62x39 specific lower. They all use a standard .223 spec type lower. Many problems can be had with these builds. First of all the gas ports may need to be enlarged depending on ammo. A carbine short system tube seems to work better. Another problems seems to be reliable mags. AK mags curve for a reason due to round design of the 7.62x39 cartridge. With that said, mags are a trial and error with no real sure proof mag that I know of. I have used a MWG and a USA mag steel ten rounder with good results. The next facet of these rifles is with the exception of Colt IIRC, most bolt faces are just a opened up .223 bolt that leaves a thin weak extactor and bolt face. I suspect this also factors in with the firing pin protrusion. While this may not give you a fix for your particular rifle, these are the areas I would look at in trouble shooting. Hootbro

Untrue, Special Weapons makes the AR47 lower that uses AK47 mags.  As much as I dislike giving them a plug- it is available.

EurasianMech,

Dude, I had the same problem with my Model 1 Sales 7.62x39 upper when I first got it.  It turns out that I was using cheap Wolf 7.62x39 FMJ/JHP and that type of round had a hard primer. All of the American 7.62x39 fired perfectly but of course, it was expensive as hell.  I finally found that Barnaul FMJ/JHP worked flawlessly. You can find it from MidwayUSA for just a little bit more than the Wolf.

Model 1 Sales does make a nice upper though. And I received it very quickly so their shipping/customer service is pretty good.  Here is a pic of the upper before I sold it:



I hope this helps.

Quoted: Untrue, Special Weapons makes the AR47 lower that uses AK47 mags.  As much as I dislike giving them a plug- it is available.

You are correct in a sense. My point and the original posters question was implied that a traditional lower was being used. The lower you mention goes beyond what is a tradional swap out upgrade and requires special machining of the upper. That is why I thought it was not relevant t the discussion. Thanks for the input.

Hootbro

Joe   The two biggest problems with an AR-15 chambered in 7.62 x 39 are magazines and quality ammunition. Magazines are a problem ,if you can find the converted AK 47 steel mags they work [these are the ones that have the top reshaped to fit the AR mag well]great other wise its hit or miss at the present time, hopefully someone will make these mags again.
US ammunition Mfg use sami specs in building the ammo and so do the gun Mfg's, the firing pin protrusion is shorter. Alot of the imported ammo uses a harder primer seated deeper for use in AK47's and SKS which have alonger firing pin protrusion. Other than domestic ammo I've had good luck with the Cheata brand 7.62 from S Africa  working in my guns and S&B brass case works fairly well also. There is no difference in the lowers made by DPMS other than the cal. markings.

Thanks for all the input guys. I talked to him today and found out the ammo we were using was of the 1961 era so aged and hardened primers are a definate possibility. We solved the magazine feed problem by using a standard steel .223 magazine. Loading is a little tight but it does atleast cycle the rounds, a little bit of dremel modification will fix this. A trip to a fairly close gun show this weekend should solve the ammo problems. Once again thank you all for the replies and valuable advice.

Joe