VFC Umarex HK53 GBBRThe Heckler & Koch HK53 is a variant of the HK33 which is basically a 5. 56mm version of the famous H&K G3 rifle but resembles more of an MP5, and uses Heckler & Koch's famous roller delayed blowback system. The HK33 was in response to the United States adopting an intermediate cartridge during the Vietnam War. However, Germany didn't adopt the 5. 56mm NATO round until the arrival of the H&K G36 rifle. The HK33 was big and even its "Carbine" variant