Action Army AAP-01 Gas Drum Magazine pistol light so you need specific battery

so you need specific battery sizes to fit properly

 Piston Teeth: 14 MIM Steel Piston Teeth

the all new H&K MP5 Competition AEG from Umarex features a full metal gearbox and is compatible with Tokyo Marui internal parts

High capacity (Hicap) magazines usually hold 150 rounds or more

Action Army AAP-01 Gas Drum Magazine pistol light so you need specific batteryThe AAP 01 Drum Magazine from Action Army gives you nearly bottomless fun on the airsoft field. This gas drum magazine holds 350 BBs, and is filled using the extra large easy fill cover. Instead of a winding wheel, this magazine uses a flash mag pull string for ease of loading. A QD sling socket on the back allows you to attach a sling to protect your magazine from being accidently dropped. The AAP 01 Drum Magazine is compatible with all TM spec