How To Pick a Zero Range For a Laser Sight
Laser sights mounted above the barrel function identically to conventional sights, but when they are mounted below the barrel, sighting becomes more complex. The main advantage of mounting a laser sight below the barrel is that the conventional sights can be retained. Such dual sight systems are available for handguns, and these systems are generally intended for use at short ranges and for self defense. The figure below shows three paths a 9mm Luger bullet would follow with respect to the line of sight depending on the sight height and the sight adjustment. Trace 1 is the pathPath the bullet would take given a conventional iron sight and a sight adjustment (12.2 MOA) that keeps the bullet inside a 2 inch vital zone for the maximum distance. Trace 2 is the path the bullet would take given a laser sight mounted 2 inches below the barrel (typical) and a sight adjustment (0 MOA) that also keeps the bullet inside a 2 inch vital zone for the maximum distance. Trace 3 uses the same sight as trace 2 but the sight adjustment (-4.4 MOA) is set to zero the bullet at 25 yards.
It's easy to see why sights are mounted above the barrel. Trace 1 goes to 94 yards before dropping 2 inches below the line of sight, while trace 2 goes to just 53 yards before dropping 2 inches below the laser beam. While not shown in the figure, trace 2 is 10.8 inches low and trace 3 is 15.2 inches low at 94 yards. Unless you want to do target shooting, it doesn't seem to be a good idea to zero at a range that results in a negative sight adjustment as is the case in trace 3. For self defense purposes it seems that the best method is to sight for the maximum point blank range with an appropriate vital zone size. However, it doesn't make sense to use a vital zone that's smaller than the distance the sight is mounted below the barrel. If you do, then the bullet will already be outside of the vital zone near the muzzle. One final note is that you can't hold over or lead a target using a laser sight unless there's something behind the target to reflect the laser beam.
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