Abstract: The invention provides a projectile locking device for a recoilless weapon whereby the projectile is positively locked in a position within the barrel of the weapon so that the projectile cannot be displaced therefrom, for example, in the event that the weapon is dropped accidentally. Previously known devices can cause significant disturbance of the gas flow, causing inbalance of the forwardly and rearwardly directed forces during a firing sequence. The present invention provides a locking device which is of small dimension relative to prior devices so that less disturbance of the gas flow is caused. The invention provides an assembly of a breakable rigid member and a resilient member, one end of which is connected to the projectile and the other end being connected to a holding device in turn connected to the weapon barrel.