Last year I picked up a Colt 7;62x39 complete upper. Put it on a DPMS lower for testing. Ammo used was my reloads utilizing new WW and Rem cases with 125 gr SP bullets. Pretty standard fare for the AK's, SKS's and the inaccurate Mini-14 I had years ago.

First range trip. USGI mags loaded with 5-6 cartridges worked fine. Then the latest production C Products 10 rounders were tried and worked perfectly. The 30 rdr got off to a good start but stopped suddenly when bullet got lodged in the throat and I couldn't get it out. End of the day for that upper as I had no rod handy.

Next trip out. Now I've got a brand new RRA lower under it. Seemed like a well built unit. This time I was only using C Products 30 rdr's. The first round loaded okay but then a feeding jam. Bullet was rammed into just below the feed ramp. For the next 10 minutes I kept trying to get this thing to function without jamming, being successful only a couple times. Frustrated I give for the day and go home to contemplate what to do next. Rounds would not feed whether fed by hand or trying to feed after a fired round.

Based on my experience with the same type feeding issue with Golani/Galil, I figured there might a dimensional issue between the lower rec and the CProduct mag. So I married the upper to my Colt lower. In racking rounds through by hand, they slip and slide like butter. Checked it out with another 30 rd mag with the same slick results. Although it hasn't been back to the range for live fire testing, I've got every confidence it's going to work perfect, it's that smooth.

Anyone run into a similar situation?

New poster on this board but have owned AR's continusly since 1977. However didn't get the BRD bug until a year ago. It's certainly a lot of fun and an occaisonal mystery/challenge.