A projectile for a weapon comprises an axially movable firing pin, an initiator actuable when impinged by the firing pin, a plurality of external peripheral fins movable from a radially inward position to a radially outward position when the projectile leaves the weapon, fin engaging means for moving each fin from the radially inward position to the radially outward position and for maintaining each fin in the radially outward position, and internal actuating means for actuating the fin engaging means to engage and thereby move the fins to deploy from the radially inward to the radially outward position as the projectile leaves the weapon.