shaped body 26 which is inwardly compressible outwardly resiliantly biased and which is symmetrical about a central longitudinal axis a the body 26 has an outwardly flared front collar portion 28 and an outwardly flared rear skirt portion 30 which are integrally joined to a central ring portion 32 the central portion 32 has an inwardly projecting curved lip 34 protruding from its inner side toward the central axis as shown in fig2 the curved lip 34 is designed to form a smooth curved forwardly concave surface against the incendiary material 18 when the seal ring 24 is installed into the jacket 12 so that no sharp breaks or corners are present against the incendiary material 18 to create a frictional pinching location during projectile assembly and during acceleration and spin up the interior front collar portion 28 of the seal ring 24 is accordingly sized to frictionally conform to the projectile jacket 12 interior profile and still maintain a smooth contour after insertion the ring 24 is designed to be installed within the jacket 12 after the incendiary material 18 is deposited in the nose end of the jacket it may be installed along with or prior to the insertion of the tubular hard.