Frankenmag?

[Victor Six Bravo]

That does look like one of the USA mags.

An Air Force SERE video series (still in use) made by a civilian company has a guy running around with a 30 round, 16" 7.62X39 AR looking at the magazine.

[RCS]

When the Chinese started to import their own manufactured semi auto AK-47, one of the calibers was 223 Rem. They had to use a special magazine becase of the length of the 223 cartridge as compared to the Soviet 7.62x39 cartridge. The 223/5.56mm is a little too long for an AK-47 magazine

[browningautorifle]

I remember those, they had less of a curve than the 7.62x39. Easy to distinguish at a distance.