G&G have shared details of their RK74 magazines:
RK74 Magazines
Be milsim ready with the RK74 Midcaps designed for the G&G RK74-CQB/E/T AEG’s. A translucent design helps you know when you are about to be out of BB’s for quicker magazine changes. A BB follower is installed to ensure every last BB feeds into your hop-up correctly. The magazine is constructed out of polycarbonate material for extreme durability. Now available worldwide.Find your local G&G Dealer
G&G