A cocking mechanism for a gun, comprising a rotary shaft, carried by the mounting and having intersecting right and lefthanded screw-threads and a coacting retractor member which, on rotation of the shaft, retracts the recoiling parts of the weapon, as a result of its interaction with one screw-thread, to cock certain mechanisms; whereafter run-out occurs under the influence of spring action accompanied by interaction between the retractor member and the reverse thread. The first screw-thread may be of slow pitch to give a mechanical advantage to the operator and the reverse thread of steeper pitch to give a mechanical advantage in favor of the springs.