My understanding of the M&P has always been that practically speaking the gun is fully cocked without pulling the trigger but technically it is DAO because there is some modicum of cocking action (although Much less than Glocks) that takes place when the trigger is pulled.... As explained here:http://mp-pistol.com/boards/index.ph...666&#entry3666
And here: http://mp-pistol.com/boards/index.ph...ao#entry318203
Originally Posted by David B.
Practically, the striker is fully cocked i.e., single action mode.
Technically, the gun is considered a double action gun because there is a small (like a few thousandths of an inch) rearward movement of the striker as the trigger is pulled all the way.
Explanation, it all lies in the shape of the sear. S&W has machined a little hump into the top of the sear right where it engages with the striker face. This little hump creates a slight caming effect causing the striker to move rearward very slightly when the sear is engaged enough to allow the striker to fall. However, this rearward movement is not necessary for the gun to fire. So why did S&W build this into the sear design? Two reasons:
1. If the striker is moved rearward even as slightly as it is in the M&P design, then the gun can be categorized as a DAO gun. Evidently this is necessary for a number of reasons, not the least of which is allowing the M&P to be more readily accepted by law enforcement agencies.
2. The hump in the sear allows the sear to move back to its full set position if for whatever reason the trigger is released after not being fully engaged. If the sear moved a little bit, but not enough to break the shot, and then the trigger is released, the sear will cam back to is full set position. This allows the trigger weight to not change from shot to shot regardless of how far the sear moved previously.
You can actually see this happen if you look through the back of your gun under the striker cap where the sear and striker engage. Make sure the gun is unloaded, and press the trigger slightly just enough to allow the sear to partially move, and rather than break the shot, release the trigger and you'll see the sear move back to its full seated position ready for a consistent pull the next time the trigger is pressed.
The exception to number 2 is that an extremely rough striker face can prevent the sear from moving back to it full set position if the trigger is released before the striker is dropped. However, this will correct itself over time as the parts smooth out with use.
If my understanding is incorrect (as explained above) and the M&P trigger technically only performs one action, then what exactly is the DAO designation based on?