Topic summary
Double-action only
Extracted from the Wikipedia article Trigger (firearms).
Double-action only
A double-action trigger, also known as double-action only (DAO) to prevent confusion with the more common hybrid DA/SA designs, is a trigger that must perform the double function of both cocking and releasing the hammer/striker. Such a trigger design either has no internal sear mechanism capable of holding the hammer/striker in a still position (so cocking and releasing have to happen in one uninterrupted sequence), or has the whole hammer shrouded and/or with the thumb spur machined off, preventing the user from manipulating it separately.