A Look at How Mil-Dot and Ballistic Reticle Scopes Work
The basics of a Mil-Dot scope at the "Mil-Dot calibrated power" (normally 10x or 12x in hunting scopes, sometimes noted as just the highest power in scope instructions) is simply this: dot to dot means about 36" @ 1000 yards, or 3.6 inches at 100 yards. Few instruction manuals that accompany Mil-Dot scopes go into useful detail. I say "about 36 inches" at 1000 yards, because it is closer to 36.000012 inches, but that is more extraneous than useful.
The actual measurement here is milliradians of angle. There is an important distinction to be made; there are two common ways to measure angle. We have just touched on "mils" or milliradians, but more common is MOA, meaning minutes of angle. It can get confusing, but if the goal is accuracy, we need to be sure if milliradians of angle are being discussed or minutes of angle. Like metric versus English units, it is just two different ways of defining measurements. There are 360 degrees in a circle, which translates to approximately 6.2831853072 radians in a circle.
Most range-finding or range-compensating reticles, like the ballistic plex style of reticle, are based on minutes of angle. This is whole different ballgame, as we can forget about radians and milliradians. One MOA equals about 1.047 inches at 100 yards. A 3 MOA ballistic plex reticle is 3.141 inches from line to line at 100 yards, 31.41 inches at 1000 yards. Not enough to fret about at 100 yards, but as both of these scopes are marketed as long range sighting systems, assuming the wrong way a reticle is calibrated can cause you to miss your varmint at extreme long range, frustrate you, or both. The whole point is accuracy to begin with, so we might as well be a bit accurate as to how this stuff is supposed to work from the start.
Mil-Dot reticles, once you get the hang of them, are far more versatile. You can holdover and hold under with equal ease, and precisely allow for windage as well. With dots all over the place, it is very easy to visualize half of a dot to dot length, or a dot and a half of length as the case may be. Mil-Dot aficionados will tell you that a Mil-Dot scope is the only "real" range compensating scope (and range finding scope) that there is. Well, they have a point, or at least a dot!
However, there is an advantage to the big game hunter and the long-range muzzleloading hunter specifically in choosing and using a more simplistic, albeit more limited design. A ballistic plex type reticle does not clog your field of view like a Mil-Dot, and hunting reality shows that in the vast majority of cases, neither high magnification nor holdover is used to take game animals. In this large majority of cases, neither a Mil-Dot nor a ballistic plex style is used or of any value.
Many feel that if you are a practical hunter, you are wise to limit yourself to the maximum point blank range of your rifle. As for closer being better, well, it just always is. Use of a ballistic plex reticle is out of the way when you don't need it, but instantly there on the rare occasion when you do. It sure beats the notion of good old "Kentucky elevation" at 300 yards.
We can also discard the 3.6 inch way of thinking for practical purposes, and just use the more intuitive (for many) 3 inches per hundred yards of range between the gates, or 9 inches at 300 yards. With fur in the crosshairs, the less optical clutter the better.
Onto a specific application and example that will hopefully give this little missive a bit more meaning. The scope used is a Bushnell Elite 3200 4 x 12 AO with Bushnell's "Ballistic Reticle." The gun: a Savage 10ML-II. The load: 60 grains of Vihtavouri pushing a .458 Barnes Semi-Spitzer (G1 of .291, Form factor .702, SD .204) at a muzzle velocity of 2287 fps.
A logical true zero is 150 yards. That makes us good to go without elevation correction to 190 yards, dropping 2.98 inches below line of sight at that range. At 200 yards, shift to the first tier of our ballistic reticle. What would put us at -3.99 inches is now actually +2.01 inches thanks to the reticle. Now we are good to go again, but for a far shorter increment out to 250 yards now at (2.5 x 3 in. = 7.5 in correction subtracted from LOS of -10.82 in = -3.32). Between 200 and 250 yards, tier one does it for us.
Beyond 250, we need to shift gears again: down to line two of our reticle. That is 6 x 2.5 = 15 inches correction at 250 yards, a line of sight basis meaning +4.18 inches at 250 yards. We shift to this 2nd line only past 250, though, and we are trajectory corrected again to 300 yards, where we find ourselves at -2.69 inches. We've not yet addressed windage, but that is a story for another day.
After 300 yards, things get ugly in a hurry. At 310 yards we will drop to the third tier. That gives us 9 inches x 3.1 = 27.9 inches of compensation. Calculated from the -23.05 LOS, we are +4.85. We can continue to 350 yards leaving us at -2.55 inches. Beyond this, we have exceeded the ability of most to accurately place a shot, and the .45 caliber trajectory (and windage) makes continuing a marginal affair for most.
Our bullet drops over 3 inches from 350 to 360 yards, and over 3.3 inches in addition to this from 360 to 370 yards. At 370 yards, just a 10 mph crosswind blows our bullet nearly two feet away from our crosshairs on a stationary target.
So, though all this must naturally be 100% range verified in your individual gun to confirm, the thought process with the 150 yard zero and the Bushnell Ballistic reticle is as follows.
Inside 200 yards, take him. Between 200 and 250, use the first line beneath the crosshairs. Between 250 and 300 yards, the second line does the proper vertical compensation. Between 310 and 350 yards, the third line makes the correct compensation.
With this reticle the length of the lines compensate for 10mph wind drift in concert with the specific tier you are on. Tier one has 3 minutes to the left and right of the vertical crosshair, tier two has six minutes on either side, and tier three has nine inches on each side.
Co-mingled with the first line above, at 200-250 yards we can easily compensate for a 10 mph cross wind. Beyond that, I believe you'll need a printout and a wind meter to have confidence in the shot. The best bet is no crosswind at all.
With this load, a 175 yard zero is better, at least for me.
+2.46 @ 100 yards
Not a bad general purpose load!
Copyright 2006 by Randy Wakeman. All rights reserved.