This is the H&K G36C High Capacity 440 Round Magazine for use with the H&K G36C (Item#:HK-2279000), Echo 1 SM-C airsoft, TSD Tactical SG-Series AEG's. Easy to fill, just pour in 440 rounds through the top hatch. Easy winding spring dial on the bottom keeps tension on the ammo for smooth feeding. Best of all these are absolutely perfect in look and feel. Not compatable with dual power G36C - HK-2261230