12" Rail on rifle-gas system - doesn't cover lo-pro gas block, just right up to it: 12" rail on carbine gas system, with 14.5" barrel - fully covers up the gas block, and the rail extends several inches beyound the gas block: 13" rail, overlapping a mid-length gas system, on a 16" barrel: 13.8" rail, coming right to the end of a lo-pro PRI gas block, on a rifle-length gas system: 12.875" rail covering a mid'length gas system: Carbine gas system, with carbine rail, A2 FSP: Carbine gas system, 9.25" rail (covers gas block): Rifle-gas, Rifle handguards, A2 FSP: Mid-length gas, mid-length freefloat, A2 FSB - rail comes right to the edge of the FSB (front sight base): Tacti-Cat. He will whoop some ass on a moments notice, despite the "gentle nature" in the pic. Expolsive power in a small package. Dangerous... :o