Originally Posted by bruce
4 grams is the bullet weight but the full cartridge is 12 grams. So, 100 rounds would be about 3 lbs.
A basic M4 with the Surefire 100 rounds mag would weight about 10 lbs.
So your still looking at nearly two pounds per magazine, even in the sixty rounders, not including the magazine weight itself. Still, weight is in the center of the gun, and that platform could still be lighter than many others. Those magazines would however create more weight in one spot on your loadout, and wouldn't do much for slimming your profile.
It's hard to say wether or not they'd be a reasonable option over the standard.