I sent an email to Robinson Arms Tech staff to learn more about the AR-15 magazines for the 7.62x39 version of their XCR-L Rifle. This is the exact correspondence that transpired, I'm sure the information will be just as useful for you as it was for me.
(Adam) "Let me just say for the record, you make a fantastic rifle, I love the design and functionality of the XCR-L! But having said that I have another message for you, A rifle this advanced, this reliable, and this durable, it deserves a magazine that is it's counterpart as advanced reliable, and durable. I don't think I need to tell the tech guys a semi-auto rifle is only as reliable as its magazine, you know that already. take a look at these links"
(Robinson Tech Reply) Unfortunately, we get the magazines from C-Products. Their quality has been iffy. I'm not sure having magpul make the magazine is the answer. Part of it is that the magazine is made for the AR-15 and not the XCR. If we made a magazine for the XCR, we could begin the curvature earlier so that therounds would flow better. Magpul probably cannot make a magazine for the 7.62x39mm round for the AR-15 because of the curvature change required. We'd like to make our own magazine for the XCR that would match the quality of the rifle. Now in all fairness to C-Products. All the magazines we're getting from them now work. I just spent the weekend with a foreign government shooting non-pretested C-Products mags. The worked flawlessly. There's also another trick. If one finds a C-Products mag that doesn't work (assuming it fits in the rifle correctly) and it has some functional problems, all one has to do is substitute a real AK47 spring for the one in the C-Products mag. I've asked C-Products to use a stiffer spring (which they did) but they wouldn't use and AK spring because it diminished capacity by a round or two. They didn't want to do this. Despite the YouTube Videos, hundreds of owners (including course instructors)are shooting the XCR on a daily basis in the 7.62x39mm caliber with ZERO malfunctions. I would still like to make my own 7.62x39mm magazine and maybe will shortly.
Technical Service Department
Robinson Armament Co.
(Sub-note) Actually, in one or three of the videos the ammo was not the problem. In the video of the person sitting down, the rifle wasn't setting off the cartridges. This was not a magazine problem. The operator did not have the heavier hammer spring in the rifle.The rifle didn't have enough pressure to cycle the rifle. I can tell by the sound. The Russian ammo makers keep changing their loads. Wolf ammunition tends to be the most trouble for us. It has very low pressure. We'd recently had to increase the size of our gas port to properly cycle with Wolf. We were testing all our rifles with Barnaul ammo which is noticeably hotter (and more accurate). We had to buy some Wolf to test with. Making a truly multi-caliber platform has been difficult. There have been many kinks to work out. Most of the problem has been the Wolf ammo and not the magazines. The same is true of their 5.56 ammo - the pressures and primer thickness seem to change on a monthly basis. If anyone has rifle that has any problem, we can fix it an make it run perfectly. We are not perfect but are getting there.