METHOD #1: The most accurate method is to input the cosine number into your ballistic software; i.e. Exbal Ballistic Targeting Software that runs on either your home PC, Pocket PC or Palm Pilot. This is because the software takes into account the trigonomics of the fact that the bullet will still travel the full distance to target, and maintain a similar time of flight.

METHOD #2 is to multiply the cosine number to your MILRAD or MOA hold for your distance to target as indicated on your data card. For example, if your moa hold for 600 yards is 11 MOA, and .87 is indicated by the ACI, you would then multiply .87 X 11 MOA, and obtain a corrected for gravity distance of 9.57 MOA. This is fairly accurate, although not as accurate as utilizing ballistic software. This is called the "Improved Rifleman Method."

METHOD #3 is to multiply the cosine number to your sloped distance. This will deliver the flat line distance to target, or what we call the bottom leg of the triangle.

If you experiment with your ballistic software, you will find that there can be as much as eight (8) MOA difference between method #1 and method #3. Method #1 is the most accurate & preferred method. Now, adjust the sight elevation knob (come-ups) on your scope, for the "corrected range".

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--SSG, 82nd Airborne Division

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By Hugo Teufel, "Angle shooting". June 2000

After reading the wind and distance to target, the slope angle of fire is one of the least understood and equally important variables of long range shooting. Whether shooting up or down at a target, the bullet will impact high due to the cause and effects of gravity.

The subject of angle shooting has been covered in a few publications, for example, Captain S., "Shooting at Elevated Targets," Tactical Shooter (January, 1999); Lau, The Military and Police Sniper, pp. 181-85; and Plaster, The Ultimate Sniper, pp.194-200. Unfortunately, many shooters do not understand angle shooting clearly. Because gravity typically is the primary variable in angle shooting, the key to successful angle shooting is to determine the adjusted range to the target. That is, the range at which gravity has an effect on the projectile. How do we determine this range? Picture a right triangle:

The shooter ("S") is on the peak of a hilltop. His target, "T", is 500 yards distant, line-of-sight, at a 30-degree angle in a valley adjacent to the hilltop. "A" is the elevated distance from the Target's altitude to the Shooter's altitude, or slightly over 263 yards, "C" is the actual range from S to T, or 500 yards, and "B" is horizontal or "adjusted" range from S to T. Recalling our high school algebra and modifying the formula for right triangles, A² + B² = C², we can calculate the adjusted range as follows: C² - A² = B². "B," in our example, is 425 yards, but we can only calculate the adjusted range if we know the elevation. However, neither our hypothetical shooter, nor we, typically will have any more data beyond the actual range to the target and the angle of elevation or depression.

What does our hypothetical shooter do? He determines the angle of depression or elevation, 30 degrees in our example, and then turns to calculus. Determining the cosine of the angle (typically read off of a chart), the shooter multiplies the actual distance, "C," by the cosine to get the horizontal, or "adjusted" range, "B." But first, he must determine the angle of elevation or depression. (Inclination or declination)

To do so, special operations forces (SOF), Marine Corps Scout/Snipers, and regular, "leg" Army snipers typically have relied upon inverted plastic protractors, with a string running through a hole placed at the center of the base, to indicate angle. Of course, using the protractor, one must read the upside down number and subtract it from 90 degrees, to determine the angle of elevation or depression. Next, the shooter must compare the angle to a chart with corresponding cosines. Taking the proper cosine, the shooter multiplies the actual range to get the corrected or adjusted range.

The protractor, as a field expedient method, is good. It is not very rugged, and it certainly is not ideal. Two other tools, based upon the same concept, are available. The first, the Slope Doper [see Hugo Teufel, "The Slope Doper," Tactical Shooter (---, 2000)] is made of aluminum and is, essentially, a reversed protractor, with the angles and their corresponding cosines, as well as the formula, on the front of the tool. The second, is the Mildot Master, which has on its backside, various angles. The shooter attaches a string and weight to the upper left rivet of the Mildot Master, allows it to hang loose, orienting the Mildot Master to the elevation or depression, to read the angle. The shooter then turns over the Mildot Master, using the slide rule that is the heart of this tool to determine the adjusted range. As well, some data books may have charts with elevation adjustments for various angles at various distances and angle cosines for various angles (e.g., T.R.G.T.-L.L.P.'s "Sniper Data Book"), and some laser range finders have the ability to calculate adjusted range.

The Slope Doper and the Mildot Master are well-designed, useful tools, and laser range finders are interesting pieces of equipment. The Mildot Master's logarithmic slide rule gives it an advantage, in that the operator need not perform any calculations on paper, or with a calculator. The shooter need only determine actual distance and angle; the Mildot Master's slide rules handle the rest. The Slope Doper and Mildot Master have one potential drawback; not being attached directly to the operator's rifle, it is possible that in reading the angle of elevation or depression, the shooter or his spotter/partner may misread the angle (a slight problem/possibility), or break cheek-weld and proper positioning behind the rifle (a much more likely possibility). And laser range finders? Experienced shooters know that anything requiring batteries will have the batteries die when the shooter most needs that piece of equipment. Better to rely on simple, foolproof tools.

What to do? A new device, called the "Angle Cosine Indicator" ( or "Green Pill"), from The Sniper Tools Design Company, may be the answer. The latest aid for snipers and practical field shooters who must engage elevated or depressed targets, the ACI still requires the shooter (or, more likely, his spotter/observer) to perform a calculation. The ACI attaches to the shooter's scope, minimizing the possibility of breaking cheek-weld and losing sight of the target.

Solidly constructed, the ACI is made from aircraft grade aluminum and anodized olive drab. The ACI is the design of Ward Brien, former U.S. military servicemen with design contributions by his friend Ping Lee.

The ACI is intended primarily for use on a scoped rifle. The Sniper Tools Company suggests using a scope ring (e.g., Leupold QRW, Badger Ordnance rings) mounted onto the scope tube, at a 90-degree angle. The ACI attaches to the ring as if it were a scope mount. The design is well executed, tactical, practical, adaptable, and convenient. It also aids in actually protecting the scope. Alternatively, the company suggests hand holding the ACI or lashing the ACI to the day scope, spotting scope, binoculars or bow. Having mounted the ACI on both my Armament Technology AT1-M24, with 10-power Bausch & Lomb Tactical, and my Springfield Supermatch M1A with10-power Leupold Mark IV M3, I urge shooters considering the ACI to consider carefully the scope ring used to mount the ACI. Too robust a ring probably will not mount on a very low-mounted scope.

How does the ACI work? When properly mounted and the rifle is elevated or depressed, the ACI (with the cosign numbers in five degree increments) bypasses the angle and, instead, indicates the corresponding cosine number of the angle of the elevation or depression. The shooter or his observer/spotter need only multiply the actual range by the cosine number to get the adjusted range. Having done so, the shooter adjusts the elevation on his scope and engages the target. If he has done everything correctly, including compensating for wind (which works along the actual distance of the shot), the shot should be dead on target.

I recently had occasion to evaluate the ACI when I went to the range with snipers from Aurora, Colorado Police Department's SWAT Sniper Team. While on the rifle, I had no problems viewing the window on the ACI. The cosine readings on the device corresponded with the angles as read off the Slope Doper and Mildot Master. Most importantly, I did not have to break my cheek-weld, or otherwise disturb my shooting position. I could stay on target, secure in the knowledge that the cosine corresponds to the angle of elevation or depression of the shot that I would be taking. The question for the day is; how do you turn a 900-yard shot into a 700? Use the ACI! It's quick, easy to use, easy to install, extremely rugged and unaffected by weather.

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