Oh, and 30 round AK steel mags run 11-13 oz depending upon the mag.
OEM 30 round VZ58 mags run ~6.5oz.
I threw a Tapco 5.56 Galil 30 rounder on the scale and it's 5.5oz, but a 7.62x39 would be at least a 25% heavier due to bullet dimensions. So that's 6.9oz, or heavier than OEM for all polymer.
Online reports for 7.62x39 Tapco AK mags are 7.3 oz.
I threw the cheaper and less durable and lighter 40 round 7.62x39 Bulgarian slabside mag on the scale (it's steel reinforced, flat sided with the bullet images, not waffles) and it comes in at 8.9oz.
And here are some more AK #s:
Mag weights (empty). All mags hold 30 rounds of 7.62x39.
Steel - early "slab sides" (Izhevsk) - 15.25 oz.
Steel - later version w/ ribbed sides (Izhevsk) - 12.25 oz.
Bakelite (Izhevsk) - 8.50 oz.
Bakelite (Tula) - 8.25 oz.
Aluminum (Izhevsk) - 6.75 oz.
Finnish 30rd black plastic - 6.3oz
(from here:
http://www.ar15.com/archive/topic.html?b=4&f=64&t=139120 )