Hi-caps

From Airsoft Community Wiki

Hi-Caps or High Capacity magazines are a type of magazine which holds more ammunition than standard. Most magazines which don't rely on a spring to push the BB's up the tube and into the gun are referred to as "Hi-Caps". They are usually powered by the tension held in a clockwork mechanism which pushes BB's up the feed tube from a large reservoir in the top of the magazine. The clockwork mechanism is wound (usually) by using a toothed wheel which protrudes slightly from the bottom of the magazine and is turned manually by the users thumb. There are "Hi-Caps" with a small hole in the side of them that you can wind up with a key that has an allen head on it and there are also battery driven magazines as well.