its really inconsistent depending on the brand of the pouches, i mean G36 mags are huge, really unnecessarily huge. It's best to get purpose built G36 double mag pouches, ESPECIALLY since your in the US you can order from here:
http://www.tacticaltailor.com/index....ROD&ProdID=297
they have a double 7.62 pouch in ACU that states it can fit 2 G36 mags. Well it can....barely....unless you wanna take off your LBV in combat to pry a mag out, get the G36 pouches lol