The HK MP7 appears to be an early prototype of the MP7 : MP7-PDW or just the HK PDW. It has a rear collapsible stock, an underbarrel grenade launcher and a holographic sight. The weapons collapsible stock remains collapsed throughout the entire Half Life 2 series and in Garry's Mod. The weapon's alt-fire launches a grenade from the grenade launcher (note that the grenades the MP7 uses different grenades rather than the throwable grenades ). This weapon is commonly employed by the Combine, although some Rebels have been observed to use it as well.