With the right tools, installing the A1 sight should be a fairly straightforward process.
To install the sight you should have a 1/16" drift punch, ballpeen hammer and a flat bladed screwdriver to fit the windage screw. It is recommended that you make a roll pin slave punch to start the 1/16" roll pin. We use a piece of round steel rod and drill a 1/16" hole in the end just deep enough to hold the end of the 1/16" roll pin near the edge.
Place the leaf spring into the corresponding rectangular slot of the upper receiver. Place the flip sight aperture on top of the leaf spring so that you can see the "L" mark of the long range aperture. Insert the windage screw into the left side of the receiver and start it into the flip aperture. Use the flat bladed screwdriver to turn the screw so that the aperture is centered in the receiver. The left side of the windage screw should be all the way in against the receiver. Place the windage drum spring in the hole on the right side and place the detent on top of it. Push the windage drum onto the windage screw and compress the detent and spring. Align the hole in the windage drum with the hole in the windage screw. Insert the 1/16" punch as a slave pin to hold then together. Use the slave punch to start the 1/16" roll pin into the windage drum. The roll pin is then set even with the windage drum.