If you want to get really, really technical The Glock 'safe action' is a double action only (the striker is cammed the last part of the way by the trigger, then released) while the M&P is a single action (the striker is only released by the trigger, it's at full #### after the slide cycles). Not sure about the Ruger, but practically speaking it's somewhat irrelevant since the trigger pull is the same from shot to shot.