G&P Aluminum MK18 Mod O RIS for Tokyo Marui M4 / M16 Series - Black

The purpose of the Mk 18 Mod 0 is to provide operators with a weapon of submachine gun size, but firing a rifle cartridge, for scenarios such as VIP protection, urban warfare, and other close quarters battle (CQB) situations. In Airsoft terms, the shorter, more compact layout allows you to make use of the full advantages of the M4s choice of accessories and modifications in package to rival sub-machine guns in agility

The standard Marui M4 AEG barrel is too short and this real steel length RIS rail will not fit unless you also install a longer outer barrel. G&P recommends the following.