Thought of this thread when I ran across this:
Sight Adjustment Tips
The first thing to commit to memory is “FORS”. This stands for “Front Opposite, Rear Same”. So, when you want to move the point of impact, you move the front sight in the OPPOSITE direction (i.e. if the gun shoots low, move the sight DOWN, opposite from the point of impact desired).
Use a brass drift, and lay the pistol on a piece of carpet or several doubled shop rags and gently tap the slide. More often than not, you'll find that you'll have to abandon “gently” and give it a “real” adjustment (i.e. a bigger hammer and more muscle.) FORS holds true for windage as well, so if you're pistol is shooting to the right, you want to change the point-of-aim (POI) to the left, thus (“Rear Same”) you'll want to move the rear sight to the LEFT.
You can calculate the amount you need to move the sights by the following:
Multiply the sight radius (in inches) by the number of inches of impact movement, divided by distance to the target in inches.
Example #1: A rifle with an 18” sight radius shooting 6” high at 100 yards yields (18”x6”)/(100 yards x (36”/yard))=0.030” requiring you to RAISE (“Front Opposite”) of 0.030” to achieve 6” at 100 yards. Conversely, you could LOWER the rear sight by the same amount to accomplish the 6” movement.
Example #2: Colt 1911 with a 7” sight radius shooting 2” low at 10 yards yields (7”x2”)/(10 yards x (36”/yard)) = 0.0389”, requiring you to raise the rear sight or lower the front sight by this amount.
Example #3: Colt Commander with a 5.5” sight radius shooting 3” low at 7 yards (7 yards = 252”) yields (5.5” x 3”)/252” = 0.0655”, requiring you to raise the rear sight or lower the front sight by this amount.