My AR-10 .308cal 20rnd mags are as heavy as my AR-15 .223cal 60rnd mags; not much difference.
7.62x51 is a bit different the 7.72x39.
And their magazines are a bit different then the AR15/16 Ak magazines
My HK 91, M1A/M14 and AR10 magazines are prime ensamples of that.