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