A WE EU17 drum magazine for airsoft pistols has a large 350-round capacity, uses green gas, and is made from a durable mix of polymer and metal. It is designed to fit a wide range of GBB pistols with the WE-Tech system. 
 
Capacity: These drum magazines have a huge capacity of around 350 rounds, which is significantly more than standard or even extended pistol magazines. This allows for extended gameplay and more firepower without frequent reloading.
Power Source: The magazines are powered by green gas and feature a large integrated gas reservoir. The fill valve is conveniently located on the bottom for easy refilling.
Construction: They are built with a durable, injection-molded polymer main body and a metal magazine stem and internals, designed to withstand the rigors of field use.
Loading Mechanism: BBs are loaded through a large side hatch, and a front-mounted winding wheel is used to wind them up to the feed lips, ensuring smooth and consistent feeding.
Compatibility: Designed primarily for WE G17/EU17 series GBB pistols, they are also compatible with other WE G-series models (G18, G19, G26, etc.) and other GBB pistols with the WE-Tech system, such as SAI BLU, ISSC M22, Lonewolf, ZEV, G&P Custom, and P80. They also fit the Action Army AAP-01 pistol.
Performance: According to some user reviews, the magazines work well and hold gas effectively, with a full tank of gas often being enough to fire all 350 rounds. However, some users have reported issues with gas leaks or the mechanism breaking after limited use, so quality can be variable.