Question re: AR-15 cartridge magazines

[JCOutlaw]

What's the difference between a 5.56mm and a 7.62x39 cartridge magazine? I'm trying to figure out how to tell the difference in dimensions between the two sizes of magazines because I have several unmarked AR-15 magazines. Thanks.

[68Charger]

the 7.62x39 mags have significantly more "curve" to them.. since that round is more tapered than 5.56... I believe external dimensions are very similar, aside from the overall curve of the mags.