A projectile launching apparatus for launching a projectile, such as a pellet, a BB bullet, an arrow, a dart and a paintball includes a linear motion converter driven by a motor, a piston coupled to the linear motion converter and reciprocally movable within a cylinder, a spring assembly and a breech assembly. The piston compresses a gas within the cylinder, after which the compressed gas expands in the barrel of the breech assembly for launching the projectile. Breech assembly includes a breech, a bolt, and bolt barrel cam, which rotate with the gas spring to allow a projectile to enter the breech and then to seal the bolt in the breech before the spring assembly releases its stored energy to launch the projectile.