The Umarex (VFC) 25rds Magazine for Umarex UMP45 GBB SMG is a polymer encased metal construction magazine and holds 30 rounds of BBs. Green gas only. If you own a Umarex UMP9 gas blowback rifle, then this UMP45 gas magazine will also work with your gun. The gas magazines of the UMP45 and UMP9 are interchangeable.