Sighting choices for your patrol rifle

The neat thing about the Internet is all the great information you can get from Web sites and discussion groups. The bad thing about the Internet is that much of the information you get there is BS. It’s pretty easy to sound like an expert in a discussion group.

Lately, I’ve seen some Internet "experts" (and some good instructors who should know better) giving bad advice on how to sight your patrol rifle (AR15/M16). To quote one I just read, “I can’t imagine an officer ever firing more than 25 yards in an urban environment, so sight your rifle for 25 yards.”

Let’s see ... several years ago in a research project I conducted for The Police Marksman magazine we found that doubling the distance from your adversary (in that study, 10 feet opposed to 20 feet) greatly improved your odds of survival. Since patrol rifles give us a dramatic advantage in distance, why not use it? I can easily imagine, even recommend, taking shots longer than 25 yards in an urban environment.  For rural cops, the shots may be longer still. So, how should you sight your rifle?

First, a brief lesson in exterior ballistics. Your line of sight (sights or optics) is a straight line from your eye to the aiming point on your target. The bullet’s flight, however, is a curve from the moment it leaves the barrel. The barrel is aimed slightly up, rather than parallel with the line of sight to compensate for the curving trajectory. This means that the bullet will coincide with your line of sight at two distinct distances. When we say our rifle is “sighted in” for a given distance, that generally means the second point of coincidence, from which point the bullet will always be below the line of sight. So, when the “expert” said to sight your rifle for 25 yards, he hadn’t thought about where the bullet would go beyond the magical 25 yard line.

If you sight your rifle to deliver the point of impact exactly on your point of aim at 25 yards, the trajectory will look something like this:

Range (yds)        Distance above or below the Line of Sight (inches)

muzzle                                - 2.5
   25                                          0
   50                                    +2.2
   75                                    +4.2
 100                                    +5.8
 125                                    +7.2
 150                                    +8.1
 175                                    +8.8
 200                                    +9.0

I think 200 yards is far enough to make the point that this trajectory is impractical beyond 50 yards.  Since the bullet starts out 2.5 inches below the line of sight on an AR, I figure we can use this rifle comfortably for torso shots for any distance where the trajectory is within ± 2.5 inches. With a 25-yard “zero” this 2.5 inch tolerance allows center mass shots from 0 to 55 yards. Beyond 75 yards, the aiming disparity becomes severe. If you remember that most trainers consider the “zero” to be the second point of coincidence, the 25 yard “zero” is actually a 350 yard zero (where the bullet drops back to the line of sight).

What if we made a slight adjustment and set the sights so our group forms 1.2 inches BELOW the line of sight at 25 yards? Those of you with some dated military experience will remember the old “Canadian Bull” 25 meter sight-in target for the M16 that used a similar sight setting. With your group forming 1.2 inches low at 25 yards, the trajectory looks like this:

Range (yds)          Distance above or below the Line of Sight (inches)

muzzle                                -2.5
     2                                    - 1.2
   50                                    -   .2
   75                                   +   .6
 100                                   +1.0
 125                                   +1.1
 150                                   +  .9
 175                                   +  .3
 200                                   -   .7 

Wow. With this sight setting, the bullet is within our ±2.5 inch center mass tolerances from 0 to 230 yards (0-55 yards with the 25 yard “zero”). Hold the sights steady, get a clean trigger break and you don’t have to worry about holding over or under to more than 200 yards. Makes sense to me. 

Let’s get even more picky. We’ll say we need our bullet to stay within a ±1.0 inch tolerance for head shots. If you’re willing to fudge the tiny 1/10th inch extra at 125 yards, my sighting recommendation produces head shot tolerances from 30 to 200 yards. Most of us should never risk a hostage-rescue head shot at 200 yards, but the trajectory is there if you can use it. With the 25 yard “zero” our ± 1.0 inch head shot tolerance is only from 15 to 35 yards. At extremely close range, under 15 yards, you will need to hold high on a head shot to compensate for the low impact caused by the 2.5 inch high line of sight - with any zero setting.

The above trajectory figures are calculated for a normal +2.5 inch line of sight (some optics sit even higher, which skews the values somewhat). They are also calculated for a 55 grain bullet fired from a 16 inch barrel. Other bullet weights and barrel lengths will differ, but not by all that much.

Most of us have to do some (or all) of our rifle shooting on 25 yard ranges. So, sighting your rifle at 25 yards is perfectly acceptable. Set your sights to form your group 1.2 inches below the line of sight at 25 yards and you’re in business. One of the AR’s biggest advantages is a very flat trajectory out to 200+ yards. The bulk of our rifle shots will probably be at 25 yards or less in an urban environment. But why limit yourself? Take full advantage of what the weapon can do.

Copyright © 2023 Corrections1. All rights reserved.