Improved gun-firing system for electrically augmenting the energy releasedy ignited propellant of the system so as to increase the velocity of the projectile as it launches from the system thereby increasing the probability that it will strike a fast-moving target. The system is generally made up of a barrel and a breech. The breech is provided with a firing chamber for receiving a projectile and an ignitable propellant. In one embodiment, the breech of the system is generally comprised of a detonator, a pair of relatively spaced pressure-responsive switches and a helically wound electromagnetic coil. A power supply is connected by an interlock to the switches and coil such that the coil is not energized until both switches close. These switches close in response to the pressure of the plasma that has been progressively formed from igniting the propellant in the breech chamber. Upon coil energization, eddy currents are induced in the plasma so as to cause further heating and pressurizing of the plasma and resulting in the projectile exiting from the barrel at a greater velocity. In another embodiment, a pair of opposed and relatively spaced electrodes of different and special construction are mounted in the breech and in relation to the chamber. Upon ignition of the propellant by the detonator in the chamber, plasma is formed therein thereby creating a sustained and expanding arc discharge between the electrodes. The arc discharge augments the plasma by ohmically heating and further pressurizing same within the chamber in the projectile velocity.