I have a Colt AR-15 with a 7.62x39 Colt upper. It runs good with Colt mags which are difficult to find and if you do find them they are going to be expensive.
I have a couple of “jury-rigged” 30 round mags that use part of an AK-47 mag with a welded sleeve on top to fit into the AR-15 mag well -- not good at all.
I recently purchased four 30 round mags stamped with what looks like a “C” followed by a forward slash that has a twig-like fork on the top then the word “Products” that has the “P” in the shape of a handgun and lastly “LLC”. Under that Newington, CT
I’ll try them out when our range reopens in nine days.