A Sportline Armalite M4 with the massive looking yet remarkable lightweight S.I.R. system fully licensed by A.R.M.S. Made famous by US special forces, the S.I.R. system was one of the very first free float rail systems that allows a customized set-up of tactical accessories.
On this Airsoft gun the SIR (Selective Integrated Rail) allows super easy access to the battery compartment in the front.