G3 30rnd magazine of unknown origin. $50 OBO. I picked it up ages ago at a shop that didn’t know what it was when I still had an old PTR HKclone, but forgot about it. Never tested it with the rifle, so your mileage may vary. Definitely takes M80 ball (7.62x51) though (see pictures), and is higher capacity than the standard 20rnd box mags. Sold the PTR ages ago, so I have no need for this. My loss is your gain!