Scram cannon

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).

Description
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.

Development
The concept of a supersonic combustion ram cannon was patented in 1988, and versions were built as far back as 1994 to research scramjet technology.