If you're an HK UMP AEG user and all about a high round count, you better grab a few extra 400-round high capacity magazines to keep those rounds headed down range. Our 400-round, HK UMP AEG magazines are made of high-quality polymer, so they don't weigh much yet hold up well under rough conditions. No one likes running short on ammo, so be sure to pick up a few extras for your HK UMP AEG before you head out to the field.