Thought I'd post some info on the new piston compatible rail I'm playing with currently since there never seems to be enough hi-res pictures of product out there. It is the Samson 4-EX Pistol Length Rail compatible with Adams Arms Piston Systems. Manufacturers Linkl Parts used: M4 Upper Receiver 7.5" Barrel Adams Arms Lite Piston Block I would use an 8" or longer barrel to allow clearance of the piston gas block adjuster with flash hiders such as the Noveske Pig. If you're using a standard A2 it will fit underneath. Beyond that, you don't need my commentary so I'll let the pictures do the rest of the talking.