A method of assembling a pyrotechnically initiated explosive projectile having coaxially arranged, a nose incendiary, a penetrator core, a high explosive, and an overall jacket. A seal ring is installed between the nose incendiary and the penetrator core to preclude relative movement between the core and the jacket during projectile assembly, acceleration and spin up from prematurely igniting the incendiary charge. The seal ring has a front collar portion which preferably has a diameter greater than that of the inside diameter of the jacket so that the collar scrapes the inside wall of the jacket during insertion to remove incendiary residual so that no incendiary can lodge between the jacket and the penetrator core.