If you decide to buy a front sight adjustment tool be sure to get the right one. There are 2 designs and I honestly don't know why. You can get a dual pin tool for around $10.
Look down onto the front sight (from above the barrel, not down the barrel from the rear [lol]) and count how many notches it has on the outside diameter of the pin.
It's going to be either 4 or 5 detents. The 4 detent pin is for the A2 sight, and the 5 detent pin is for the A1 sight.
Here is a link to a page showing the tool. (3rd picture down)
http://www.gunaccessories.com/AR15-M16P ... Access.asp