Abstract: A cylinder lock for a revolver adapted to be positioned entirely within the body of the revolver to release the cylinder during cocking of the revolver hammer and to lock the cylinder against turning during firing of the revolver and when the hammer is in a forward position. A locking bar has a cylinder engaging lug on one end and is pivotally connected adjacent its other end to the frame handle of the revolver. A spring loaded pin carried by the hammer moves the locking bar such that the lug is moved out of a notch provided therefor in the cylinder to allow rotation of the cylinder and the pin is then moved into an enlarged notch on the locking bar and is cammed into the hammer to allow the lug of the bar to be biased by a spring at the other end of the bar into position in a new notch of the cylinder. After the trigger is pulled the pin is biased from the hammer to again be in position to move the locking bar.