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Reticle rangefinding.

RIFLESCOPES OFFER A SIMPLE WAY TO CHECK OR COMPUTE RANGE. HERE'S HOW.

Sometimes it seems rifle shooters went directly from "guesstimating" ranges to laser precision, but before lasers there was a more accurate alternative than guessing. More shooters should probably know how to use it, just in case their laser doesn't work, or as a check on laser results.

Reticle ranging is based on a principle of geometry called the subtended angle, defined as "the angle formed by an object at some external point." Any reticle subtends a certain angle at certain ranges. Let's say we're using a simple plex-type reticle, and aiming at a typical target marked in 1-inch squares at 100 yards. As an example, we'll say the tip of the reticle's bottom post is 6 squares (6 inches) below the crosshairs. This is called subtending 6 inches at 100 yards.

If we aim at the same target at 200 yards, the tip of the bottom post will be 12 squares below the crosshairs. This ratio of distance-to-reticle (angle) is consistent with range: At 300 yards the distance from crosshairs to post will subtend 18 inches, at 400 yards 24 inches, at 500 yards 30 inches, and so on. If we know the size of a target we can use this basic geometric principle to measure range, and even if the target's size is only approximate, we can come up with a much closer estimate than simply "guesstimating."

When I started shooting as a little kid in the 1960's, most hunting scopes still had plain crosshairs, useless for reticle range estimation. As a result, most hunting "experts," whether our Uncle Fred or the columnist in our favorite magazine, suggested various ways to estimate range. Perhaps the most common was to break the landscape down into imaginary football fields, because a football field was 100 yards long (They also assumed any red-blooded American kid frequented a football field.)

Unfortunately, most of the earth isn't dead-flat and marked off in yardages, but this useless piece of advice showed up repeatedly, apparently because the gunwriters of the day all copied each other (This still happens, but not as blatantly.) Occasionally somebody warned us distances appear different in "clear Western air," because most gunwriters, along with most people, lived in the East.

While it's possible to get pretty good at estimating distances, I never ran into anybody who did it by imagining football fields. Instead they got good by estimating the distance to a certain object, then measuring or pacing the actual distance to test their guess. This guess-accuracy, however, is normally only possible in pretty flat country, when looking at familiar objects. I became very good at it when guiding pronghorn hunters in the 1980's, before civilian laser rangefinders appeared, and could usually guess the range to a buck within 25 yards out to 400. But the skill didn't transfer to mule deer in mountains, and I wouldn't bet my ability today.

KEITH'S METHOD

Eventually I found a plex reticle was more accurate, and I learned how primarily by reading Elmer Keith, a former GUNS columnist. Perhaps because Keith was also a good long-range target shooter, he was the one hunting writer of the period who discussed using a scope's reticle to estimate range. For pronghorns he suggested a scope with two parallel horizontal a heart shot crosshairs. They could be used for estimating range, and the lower crosshair as a secondary aiming point at longer distances.

Here in Montana (and in Keith's Idaho) a mature pronghorn buck usually measures about 15 inches from the bottom of the chest to the top of the back. This is not around the curve of the body, but viewed directly from the side. A plex reticle subtending 6 inches at 100 yards brackets a buck's body at 250 yards, about as far as most "pilgrims" from back East could reliably hit a pronghorn, and the plex reticle on the 3-9X scope I used on my backup rifle just happened to subtend 6 inches when set on 6X. (The rifle itself was a very accurate Remington 722 in .257 Roberts, inherited from my paternal grandmother.)

Over the next few years my scope's reticle helped several people take pronghorn bucks they probably would have missed, and helped me take some of my own, including my then-biggest at 430 yards, as well as finishing off a buck at 550 yards, wounded by a client. Those aren't exceptional ranges today, but back then they were pretty long, especially for 1-shot kills. (Here I should admit my .257 was handloaded on the warm side, and sighted in dead-on at 300 yards, helpful in those "pre-turret" days.)

However, not everybody believed the reticle. Even after I gave them the range, some hunter shot over because the buck "looked" farther away, so they held higher. But another example occurred a decade later when hunting caribou in Alaska. I'd hunted caribou twice before, so knew a mature bull's chest measured around 2 feet. My hunting partner had first shot, and when we found a good bull on a mountain ridge, I used the scope on my rifle to estimate the range at about 325 yards. Our guide decided he and my partner could crawl a little closer, so they did--about 25 yards.

It turned out this little crawl was so the guide could whisper I was full of it, since the bull was only "200 yards" away. My buddy believed the guide, and held in the middle of the caribou's chest, since his .30-06 was sighted-in at 200 yards. The bullet broke the bull's leg just below the chest, but a quick second shot, with the reticle held high enough for 300 yards, finished it off.

This is the same basic principle of mil-dot reticles as used by snipers before laser rangefinders. They knew how tall their human targets should be, and framed them with the dots. Mildots make this relatively easy, since they're spaced 1/10th of a milliradian apart. Instead of estimating how much a single gap (such as the space between the crosshairs and top of a post) should cover at any range, counting the dots provides the information. This is why first focal-plane reticles are handier for range estimation: The subtension of the dots never varies, no matter what magnification the scope is set on.

Knowing how to reticle-range has helped my field-shooting enormously on several occasions, even after laser rangefinders appeared. Average hand-held lasers don't always tell us the exact range, especially on level ground like a wide pronghorn prairie, since they can end up ranging a sagebrush in front or behind a buck. On one elk hunt a laser happened to range the top of a tree near the line of sight to a distant elk, but I double-checked the range with my scope reticle, and found it was about 50-percent longer than the laser said. On at least two deer hunts there simply wasn't time to use a laser and then switch to the rifle, and the reticle did the job. It's a good technique to practice, and aiming at 100-yard target marked with the common 1-inch grid reveals what you need to know.

Half of John Barsness's 12 books are on firearms and shooting. His most recent, Modern Hunting Optics, was published by Deep Creek Press in 2014, and is available through www.riflesandrecipes.com, P.O. Box 579, Townsend, MT59644, (406) 521-0273.

TYPICAL CHEST DEPTHS OF MATURE BIG GAME ANIMALS

ANIMAL                                    SIZE (INCHES)

Pronghorn, buck or doe                         15
Whitetail buck (southern)                      16
Whitetail doe (southern)                       14
Mule deer or northern whitetail buck           18
Mule deer or northern whitetail doe            15
Bull caribou                                  28-24
Bull elk                                      28-30
Cow elk                                       22-24
Shiras or Canadian bull moose                 30-32
Alaska-Yukon bull moose                       36-40
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Title Annotation:OPTICS
Author:Barsness, John
Publication:Guns Magazine
Date:Aug 1, 2015
Words:1296
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