The scram cannon is a hypothetical kinetic energy weapon based on ram accelerator technology. The scram cannon uses a projectile that uses supersonic combustion ramjet technology to increase the Muzzle velocity to levels that are impossible with normal gunpowder based guns; firearms are limited by the speed of sound in the propellant gases, which limits the velocities to about Mach 5 (see internal ballistics).
A scram cannon uses a sealed barrel filled with a fuel/oxidizer mixture that undergoes supersonic combustion as the projectile passes by. The energy liberated by this combustion acts to propel the projectile through reaction, like a jet or rocket engine, rather than by pressure as in a gun. This allows the scram cannon to launch sizeable projectiles at velocities previously only attainable with railguns, light-gas guns and rockets, but with significantly simpler techniques. Scram cannons often show up in science fiction and role-playing game discussion boards.