Removing and installing the A2 Rear Sight can be done by following these simple directions:
Remove the lower receiver, bolt carrier and charging handle. Drive out the roll pin under the elevation knob with a 3/32 drift punch that retains the elevation spring. Catch the elevation spring when removing the drift punch. The A2 sight base can then be removed by turning the elevation knob clockwise. There will be a ball detent and a detent spring in the left side of the sight base that will also come out when removed so do not lose them. The two piece elevation knob will now slip out the side of the receiver. Here again is another ball detent and detent spring for the elevation knob that should be set aside. The index screw may be removed from the top index knob with a 1/16" allen wrench.
Place the index knob on top of the windage elevation knob. Place the elevation spring and ball detent in the hole in the receiver then slip the elevation knob assembly into the slot in the receiver for it. The ball detent and spring may be compressed with a small flat bladed screwdriver until the elevation knob captures them.
Start the 3/32" roll pin into the receiver just below the elevation knob. Turn the receiver upside down. Place the elevation spring into the sight base. The elevation spring must be compressed when installed. To make this easier the rear sight base elevation can be turned out about 22 clicks from the bottom but not so far that the slots in the threaded base do not line up with the retaining pin hole in the receiver. Compress the elevation spring with a small flat bladed screwdriver and tap in the retaining roll pin until the spring is captured. The roll pin must be on top of the spring and not pass through it. Tap the roll pin in with the drift punch until it is flush with the receiver.
Turn the elevation knob so the sight base is all the way down to its last full click. Then turn it up one click and hold the lower elevation knob in that position while slipping the upper index knob around until the 8/3 index lines up on the left side of the receiver. Place the sight index screw on the 1/16" allen wrench. Then insert the screw into the hole in the sight base just ahead of the rear sight aperture. Turn the screw into the elevation knob until it bottoms out and locks the index knob to the elevation knob. Remove the allen wrench and check the elevation knob to see that moves without binding.