Lighweight rail system that at SKDTac that you can use for M4 PTWs or Gas Blowbacks... "The VTAC Extreme BattleRail is an one-piece, free floating rail for AR15 systems. The unique lightweight design helps reduce heat transfer and allows for a faster target acquisition. The rail is easy to install and features an uninterrupted top M1913 rail that allows the mounting of optics and backup iron sights. TROY designed a barrel nut specifically for the TRX rail meeting a tighter tolerance which will reduce stripping the barrel nuts altogether.

Features:

• New state of the art rotary locking system
• Proprietary patent pending one-piece design
• Free floating design
• Continuous, uninterrupted top rail
• Installs in less than two minutes
• Reduced heat transfer
• Significant weight reduction
• True U.S. Military Specification M1913 rails 
• Increases target acquisition speed
• Free floating design that enhances accuracy
• Comes with one 4in and two 2in quick attach rails
• Weight: .7 lbs."