Neither does a FA parts kit and FA BCG as you had stated in your earlier post.
The sear is inteagral to full auto operation!
Not at all. It is only 'integral' to the 'properly timed' full auto operation'.
Please indulge me for a moment.
1st, remove the upper from your AR and deal with the lower only.
With the (F/A) selector ( all fire control parts being F/A) in the fire position pull the hammer back with your thumb until it locks in position. It is being held in position thru the engagement of the front of the (F/A) trigger unit with the little lower hook in the back of the (F/A) hammer. If you were to squeeze the trigger at this point (and not release the pressure, the front of the trigger would rotate down away from the hammer hook and allow the hammer to move foreward to the normal firing positon. If you continue to squeeze the trigger and pull the hammer back as if the carrier was recocking it, the hammer does not catch on the front of the trigger now as it is still rotated out of the way, but does catch on the (F/A) disconnector hook at the middle hook of the hammer. The disconnector locks the hammer from returning foreward (to hit the firing pin) and stays locked until you release the trigger which allows the hammer to pop off of the disconnector at the same instant that the lower hook reengages the front of the trigger, and is ready to fire again.
Now rotate the sector to the F/A position and again pull the hammer back with your thumb. Again it is locked in place exactly as it was in the semi auto mode. This time if you were to squeeze an hold pressure on the trigger, it would fall foreward as before, but now on it's return travel it will not lock with the disconnector hook as the disconnector has been rotated backwards on its axis by the repositioning of the selector. With your thumb you can now move the hammer fully backwards and fully forewards at ease and can do so until you release the trigger again, where upon it will engage by the lower hook with the front of the trigger.
If you had a sear (DIAS or Mil spec) installed, it's ONLY function is to engage the top hook of the hammer and hold it back (to keep it from free firing) until the F/A carrier trips it and releases it to fall foreward to strike the firing pin. IF the trigger is released during the process, the carrier will trip the sear which again disengages from the top hook of the hammer. The hammer though immediately gets caught by the lower hook engaging with the front of the trigger and is not allowed to fall foreward.
Without the sear the only mechanical difference in operation is that the hammer (being able to freely rotate back and forth without hooking anywhere) will be rubbing up against the bottom of the carrier as it speeds by and eventually is allowed to fall fully foreward and will/can contact the primer with sufficient (heavy spring) force to fire the cartridge. On a genuine F/A carrier there is NO exposed collars of the firing pin to jam the hammer. The risk of an out of battery occurance is slim (but real), as the locking lugs should be fully rotated just prior to the carrier being far enough foreward for the firing pin (which has the force of the hammer behind it) to be contacting the primer.
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