Slow cook off rocket igniter

A gas generating propulsion system includes an igniter containing an igniter propellant and an auto igniter. A rocket motor is coupled to the igniter and has a housing containing a main propellant, a rocket motor throat and a nozzle. A release port extends through a portion of the rocket motor. This gas release port has a variable diameter through bore in fluid communication with the main propellant. In this way, the through bore has a variable area that forms an unobstructed open area with a cross-section effective to discharge gas generated by the main propellant such that a pressure increase within the housing remains below a safety value for the housing.