Before we head for the range let's check the operation of the AR-15 safety. Pull the charging handle all the way back, check the chamber, then release it.
Now rotate the safety to the safe position and pull the trigger. The hammer shouldn't release.
Move the safety to the fire position and pull the trigger. Now the hammer should release.
Pull the trigger back and recock the hammer.
Now, slowly release the trigger and listen.
As the disconnector releases the hammer and is caught by the sear. Now squeeze the trigger and the hammer should fall.
Repeat this test several more times before you head for the range.