a firing mechanism in which the hammer and trigger are interconnected by gears , so that the hammer can be cocked and fired simply by pulling the trigger in what is commonly referred to as double - action . the hammer is mounted so that it can pivot independently of the gears in order to discharge a cartridge . a sear connects one of the gears to the hammer so that it can be cocked by means of the trigger and then released when the trigger is fully retracted . a safety feature is also provided by mounting the hammer so that it is normally out of alignment with the firing pin and , thereby , can not accidentally discharge the gun . however , when the trigger is pulled the hammer is shifted bodily to bring it into alignment with the firing pin .