The invention relates to an increment charge (4) to be placed around a tail shaft of a fin-stabilized mortar projectile (1), the increment charge (4) having a centrally located space for the tail shaft and a mounting opening in the space for mounting the increment charge (4). On the opposite side of the increment charge (4) there is provided a protrusion that fits into the mounting opening of an adjacent increment charge (4) for locking them in relation to each other.