The ASG LMT Defender 4 S.I.R. All Metal AEG 6mm Airsoft Carbine is an extremely well made M4 styled Airsoft Carbine. The LMT is fully licensed and utilizes the S.I.R. Rail system for easy customization of just about any accessory you can think of. The LMT Defender 4 S.I.R. is not just amazing looking but also has teh internals to back it up with 8 and 9mm bearings all ready for Li-Po batteries if that's what you're into!