Horus Vision Asli 6v3c3l

FOG HORN a Twobirds Flying Publication

Horus Vision ASLI™1 01 Nov 2010

By: Sal Palma ( Follow me on Twitter www.twitter.com/twobirdsflying ) One of the more intensely debated topics, in precision rifle, is acute angle shooting. As of this writing, only the U.S.M.C. trains snipers in acute angle firing and requires the Scout Sniper to attend a dedicated school; yet all know the importance of its understanding. As military or law enforcement snipers, why should we concern ourselves with acute angles? The non-rigorous answer is that it will make the difference between a hit or a miss, at distances of 500 meters or more. However, acute angle shooting is also critically important when only a small portion of your intended target is exposed. For example, the human head is approximately 7 inches wide and 10 inches tall. So, let's say you find yourself having to engage this target at a range of 400 yards firing from an elevated position. The inclination angle is 30°; let's disregard wind for this example. The elevation required to make this shot, without considering the angle is 7.9 MOA. However, if you take the inclination angle into consideration, as you should, your correct elevation setting is 6.3 MOA. If we subtract 7.9 – 6.3 we see that there's a difference of 1.6 MOA; that difference, at 400 yards, translates to a point of impact error of 6.4 inches. If you were aiming for the “T” you will more than likely miss your target; however, you'll be on hand to watch as he detonates the dirty bomb. A number of very highly regarded professionals have written on the subject; producing material ranging from scholarly treatise to just simple and informal discussions. I tend to favor simple explanations because they are easier to , and the objective is to provide the sniper with the tools to successfully engage and defeat the target. For that reason, I will avoid discussions of gravity, as it is a 1

ASLI™ is a Horus Vision, LLC trade mark.

Copyright 2010, Sal Palma, dba Twobirds Flying Publication, All Rights Reserved

constant, and in virtually all fields of science we don't correct for a constant we simply take it into . In discussing ballistics, gravity is a constant present along the projectile's flight path. However, the variables influencing ballistics (the shape of the flight path) are aerodynamic properties of the bullet (ballistic coefficient), muzzle velocity, mass, temperature, altitude, wind and wind direction, humidity, and in extreme long range shooting, we consider the earth's rotation (angular velocity) because the projectile's flight time, to the target, is significant with respect to the earth's rotation at its surface for a given latitude. Precision or sniper rifles are zeroed on the horizontal plane. That is, at 0° relative to the horizon. This is the rifle's point of reference or baseline. When we shoot at acute angles we are shooting at targets that are significantly above or below the horizon; a positive angle means that you are shooting uphill, and a negative angle means that you are shooting downhill. Because your rifle is zeroed on the horizontal plane, we need to convert the line of sight range (this is the range as obtained from, say an LRF, along the inclination angle) to the target, to the equivalent horizontal range - think of this as translating from one language to another. For example, if the line of sight range is 600 yards and the inclination to your target is 30° your equivalent horizontal range to the target is determined by the following formula: (Line of Sight Range yards/meters) x (Cosine of the angle). In our example, the calculation is 600 yards x .87 or 522 yards. The sniper then uses the appropriate elevation setting for a range of 522 yards but not 600 yards, to engage his target. It follows from this discussion that determining the shooting angle as accurately as possible is key in developing a good firing solution and hitting your target. In the past, snipers used bulky and inaccurate inclinometers made of plastic or cardboard; not only were they awkward, but they required the sniper and his spotter to interpolate inclination angle measurements. Once the sniper determined the angle, he either referred to a trig table and performed a manual calculation, or he referred to his dope book for the elevation setting corresponding to the target range and inclination. This process is time consuming, laborious, and prone to error. Today, the military or law enforcement sniper has a better tool to assist him with acute angle firing. The ASLI™ or Angle, Slope, Level Indicator, designed and manufactured by Horus Vision, LLC of San Bruno, CA, is such a tool. Horus' ASLI™ combines an inclinometer with a cant / level indicator that addresses the need for fast and accurate target inclination measurements, and a level to ensure that the sniper has eliminated cant from the rifle – in other words, the vertical stadia on the weapon's optical sight is perpendicular to the earth's surface. The ASLI™ provides the sniper and his spotter with an easy to see inclination angle and the corresponding cosine value, as shown in the picture below. The numbers on the inside of the wheel provide the inclination angle; the numbers to the outside indicate the cosine value for the corresponding angle. The picture on the left shows a 0° inclination corresponding to a cosine value of 1. In Copyright 2010, Sal Palma, dba Twobirds Flying Publication, All Rights Reserved

this case, the line of sight range to the target is the same as the equivalent range. However, if the inclination angle were 100 the cosine of the angle is given as .98; here, the line of sight range differs from the equivalent range and the sniper must use the elevation setting corresponding to the equivalent range in order to achieve an accurate shot placement. By using an ASLI™ mounted to his optic or on the spotter's optic, the sniper team can readily and accurately determine the inclination angle and its cosine value without the need for trigonometric tables or scientific calculators. Angle measurements are accurate to 2°. Equally important to long range precision shooting is cant. Using the ASLI's™ level indicator, the sniper can quickly see that his weapon has a slight cant – as shown in the picture above – and quickly correct. The ASLI™ can be mounted on any 30mm or 34mm tube using the mounting ring supplied. The tube diameter must be specified at the time the order is placed. Using the ring supplied, the ASLI™ can be mounted on either the left or the right side of the weapon sight. It can also be mounted with the level indicator up or down, so there's a great deal of flexibility. Horus also offers a Picatinny rail mount so that the ASLI™ can be attached to any compliant rail, for example La Rue’s SPOTR system or on the weapon's own rail underneath the scope's tube. Horus designed the ASLI™ to be self calibrating. Simply mount the ASLI™ so that the level indicates plumb and you're good to go. There is no need to zero the ASLI™. The installation process is error free and exceptionally simple. However, ease of use and installation by themselves will not win the day. Military and law enforcement sniper platforms have to withstand harsh conditions and rough handling. Here too the ASLI™ meets and exceeds all expectations. The enclosure is made from a clear high-impact polycarbonate that will withstand the shock from a weapon drop. The instrument is dry nitrogen purged, dust proof and waterproof to 20 meters. The indicator wheel is made of precision machined aluminum to a tolerance of ± .004”, all markings are laser engraved . The indicator wheel is magnetically dampened to prevent wild oscillations with the slightest movement. Horus also provides a rubber cover to further protect the ASLI™ . There's been some criticism of Horus' ASLI – mostly made with comments not well reasoned – regarding the lack of illumination. To address that concern, you need to keep in mind that the ASLI is a critical component used in a targeting system for tactical application. It is a sub-assembly, in a complete solution that includes reticle patterns and ballistic software. Under most circumstances, tactical situations require some degree of stealth; therefore, illuminating the ASLI is undesirable. First, it exposes the team to detection and finally, it would degrade the snipers night vision; both of which are unwanted artifacts.

Copyright 2010, Sal Palma, dba Twobirds Flying Publication, All Rights Reserved

Closing Comments Horus Vision ASLI™ is an indispensable tool for anyone fulfilling the role of Sniper or Designated Marksman. Without it, precision is unnecessarily difficult to achieve at the level your job or deployment may someday require. The ASLI, when incorporated into a total targeting solution, like that designed and sold by Horus, adds a measurable level of precision that belies its modest cost of $70. The instrument is robust, reliable and well thought out. Once mounted you can confidently rely on its speed and accuracy, regardless of the weapon platform. The ASLI™ is easy to mount and to maintain, so it doesn't place an added burden on the . It is the best technology that you can get – set it and forget it! If you are unfamiliar with Horus Vision or the Horus system, I suggest you drop by their website, http://www.horusvision.com/ , you'll find it concise and informative with all of their product manuals available for , if you need a comprehensive overview of features and functions. Horus Vision, LLC has been on the leading edge delivering solutions that enhance the performance of tactical operators and their weapon systems. Much of their success is attributable to their open dialogue with those charged to perform the task.

-SP

Copyright 2010, Sal Palma, dba Twobirds Flying Publication, All Rights Reserved