A captive piston projectile (40) comprising a payload housing (43), a piston assembly attached to the payload housing (43), and actuation means (46) for urging the piston assembly from a stowed configuration to an extended configuration. The piston assembly comprises a tubular piston member (41) attached around the periphery of the payload housing (43), the attachment optionally being in the form of a circumferential groove (42) within which the piston member (41) can slide. This provides increased thrust whilst maintaining payload volume. Particularly suited to use with barrelled weapons, and also relates to a method of manufacture.