Umarex HK53 Gas Blow Back Rifle Black Magazine Eu17 meaning if you wanted to Mag meaning if you wanted to stretch the performance of this rifle out with a few choice upgrades you can Both the HK Style stock storing the battery and the pistol grip were made from polymer Fully Licensed by Umarex & H&K the best example for this is the British armed police and armed forces adopting the rifle as the L101A1 as some units mainly units that were quelling the Troubles such as the legendary Special Air Service (SAS) were armed with the HK53 as it has the same manual of arms and size as the MP5 yet it can deliver more stopping power and could deal with combatants with body armor