The Power of Performance

Archive for October, 2010|Monthly archive page

Long Range Sniping

In Message From Jeff on October 20, 2010 at 9:08 pm

Long range is a relative term. For purposes of this lesson on Law Enforcement Sniping, we will discuss ranges of 0-600 yards. No LE shot in history has been over 500 yards. A law enforcement sniper has to take into account means, opportunity and jeopardy when making lethal force decisions and so we must be able to articulate why we needed to take a shot at that distance. We also have to be absolutely certain of target ID. With those things out of the way, we can discuss how to hit at those distances. I will assume that all students to this lesson already fully understand operation of their rifle, including how to make scope adjustments for elevation and windage.

There are two primary elements to hitting a distant target. These are elevation and windage. These have to do with the major factors in shooting, the effect of gravity and drag of the air on the projectile causing it to slow and drop as it travels down range, and also the effect of wind pushing the projectile off course as the bullet travels down range at a continually slowing velocity. Let’s take these elements one at a time starting with elevation. This requires compensating for the trajectory of the projectile as it travels down range. This is the easy part of the problem, because as you will learn, trajectory is a relatively predictable factor. It will do very nearly the same thing for every shot. Trajectory is primarily influenced by the efficiency of the bullet moving through the air (known technically as its “BC” or ballistic coefficient) and the starting velocity of the bullet. Both of these things are known to a pretty high degree of precision, so the biggest variable in calculating trajectory is range. Put another way, “Where do I have to hold, or how much do I have to compensate to make sure the projectile strikes the intended distant target as the bullet is being pulled to the earth?”

You are fortunate here in that there are several ways to get the answer without having to do complicated math. There are a number of ballistic calculators out there that will do it, there are a number of sources of  ballistic informational “dope” cards available (and you will be issued one as part of the RC/PC SRT sniper Element) but the very best way is to take your rifle with your ammo to a range in your area and actually shoot a the distances you need to know the “dope” for and record your results. This gives you actual vs. predicted results and is the information you need to rely on. There are many small variables in predicted data. Even so, dope cards and ballistic printouts are usually very close and can get you on target while you refine the actual data for your own rifle.  (An example of one such “dope card” is attached for your use).

Elevation adjustments for varied ranges
There are two ways to adjust for the curved trajectory of the projectile as it travels down range. These are “holdoff” and “dialing the dope”. Let’s start by assuming a zero of 100 yards with your rifle. This means that the bullet exits the muzzle of your rifle appx 2” below your line of sight (where your crosshairs indicate). The scope is adjusted so that the point at the center of the crosshairs and the fired projectile will converge at 100 yards. The muzzle of the rifle is actually pointed at a slight upward angle compared to the line of sight in order for this to happen. At very close distances the point of impact will thus be nearly 2” below the crosshairs. At 25 yards the bullet will have risen to be only about .6” inches below the crosshair. At 50 and 75 the bullet will be so close to your point of aim as to not be worth adjusting for. The point of impact will coincide with the point indicated by the crosshair at 100 yards.  At 125yds you will be about .5” low (or appx .5 MOA) as the bullet drops due to gravity and at 150yards you will be about 1.3” low (or appx .75 MOA). For these distances you may decide to not dial any adjustment, and instead just allow for the strike of the bullet. (I personally “hold off” at ranges to about 125 yards and then start “dialing in” adjustments to compensate for trajectory changes beyond that point.) Beyond 125 yards I recommend the LE sniper dial the scope to adjust for the path of the bullet, if he is in a static position where he can do this.

For ranges greater than this I recommend sniper memorize their “Dope” in even increments of 100 yards from 100-600 yards. You may ask “Why? I have a nifty little dope card that tells me what adjustments to make!” That is true except for the fact that the card is a crutch, a backup plan, and a training aid. In a real situation it will be dark, the card will be lost, or in your back pocket under your coveralls and BDUs, or the situation will be occurring so rapidly that you need to have the answer available without looking at the card. If you memorize the calculations needed for a 200,300,400,500, and 600 yard shot you will have the answer available to you almost immediately, and without looking at the card. For distances between these numbers simply interpolate from the know rage “dope” to get the answer. Your dope might look like this:

Range/ MOA Correction

100 yds-0 MOA

200 yds-2 MOA

300 yds-5 MOA

400 yds-8 MOA

500 yds-12 MOA

600 yds-16 MOA

I suggest you also write or tape this simplified information on the side of your stock.

We have now covered the “easy part of the equation”, trajectory compensation or adjusting for the drop of the bullet. There is more to this, especially as the range increases, but if you have a good grasp so far, you are good to go out to 600. (We will cover details such as temperature, altitude, elevation angles, and humidity in a subsequent lesson plan. They are relatively minor variable for the law enforcement sniper due to the limited rages LE snipers will engage at.) We move now to the toughest external variable, wind.

Adjusting for wind
Adjusting for wind is tougher than adjusting for range, because wind is not constant. It varies in speed and angle, it varies from one moment to the next, and it increases in effect as range increases and the bullet slows. Terrain may affect wind. You may feel no wind where you are in a sheltered position, but it might be blowing 15 or 20 miles per hour downrange. It is impossible to make a perfect wind call because by the time you get it calculated perfectly the situation has probably changed. What is important is to make a quick but accurate assessment of current wind and its estimated effect and get the shot off before conditions change. How can you do this? The first step is to purchase a wind gauge. (I personally like the Kestral brand. It is relatively inexpensive, compact and accurate.) You cannot calculate for a given wind speed unless you know what the wind speed is. Practice with the wind gauge, the same way you train with a radar unit. Guess the speed and then check your guess. You will become good at estimating wind speed amazingly quickly. You now have two tools for checking wind. The wind gauge and your experience shaped by working with the wind gauge. There are other methods such as watching flags, grass, mirage, smoke and blown items. Those are good also, and should be used in conjunction with the gauge and perceptual experience in judging the wind by feel, as the sniper increases his skill. Let’s now assume that you can determine the wind speed. Remember that you are measuring the wind speed only at your location, while the wind will affect the bullet the entire distance to the target.

Now that you can calculate wind speed, you can calculate wind effect. The military has a formula for this, but I won’t teach it to you because no one actually uses it outside of sniper school. It is too complicated. I will teach you a method that is much easier, doesn’t require a calculator, and can be done in the field while you are looking through the rifle scope.

The “Black Hills” or “Range Minus One” formula
This method has three steps. It bases all calculations on the effect that a 10 mph wind will have on a .308 bullet at any given range. Once you know the range, a very simple calculation provides you the effect a 10 mph wind would have at that range. You then make two adjustments to that base calculation.

1) Adjust for the actual wind speed, because all winds are not 10mph winds.

2) Adjust for the wind value based on its angle in relation to the direction of the shot you are about to take.

The base formula for determining the wind effect on a 308 bullet is: Range (expressed in hundreds of yards), minus 1 equals the MOA of correction necessary for a 10 mph wind at that range. I.e. for a 500 yard shot in a 10 mph wind you need 4 MOA of wind correction. (5-1=4). It is that easy. For a 300 yard shot in the same conditions you need 2 MOA (3-1=2).

You now need to adjust for actual wind speed. Wind will move the bullet way from its flight path an amount directly proportional to the speed of the wind. A 5 mph wind has one half the effect of a 10 mph wind. A 15 mph wind will have 50% added effect. A 20 mph wind will have double the effect. Simply adjust your base calculation accordingly. Note that this formula works from 200-1000 yards. (At 100 yards a 10 mph full value wind will blow a typical .308 sniping projectile about .7 inch. Use that information rather than the formula for shots of 100 yards or less) For ranges that are in between even 100 yard range increments, round to the nearest 100 yards.

The last factor is wind angle. A full value wind is a wind that is blowing at 90 degrees to the path of the bullet. It will have the most effect. A wind that is blowing perfectly along the path of the bullet, either with the bullet or against the bullet will not blow the bullet sideways. It is called a no value wind. A wind that is blowing at a 30 degree angle off the path of the bullet is a half value wind. Many sniper schools do not break wind calling down past those three wind calls. They lump everything that is not full value or no value into a half value category. This might be close enough for short range shooting, which almost all LE shooting is, but understand that it is a generalization used for speed and simplicity and a more precise examination of the wind angle will provide better precision needed for longer range targets. A wind table is attached which shows a more accurate representation of wind values. Let’s go with these three values for now and give some examples of how to use the formula.

Problem: a 500 yard shot with a 10 mph full value wind. Solution: 4 MOA  (5-1= 4 MOA the wind is 10 mph and full value so no further math is needed).

Problem: A 500 yard shot with a 5 mph full value wind. Solution: 2 MOA. (5-1=4, but because the wind is 5 mph, not 10 mph you must divide your base answer by 2 to get the answer of 2 MOA)

Problem; A 500 yard shot with a 5 mph, half value wind.  Solution: 1 MOA (5-1=4, then 4/2=2, then you must reduce the answer further because it is a half value wind 2/2=1 MOA).

This is the simplest method I have found. With practice it is very fast, and it is accurate to within a half-minute at 1000 yards.

This is a quick course in how to accurately shoot at long distance. You must:

Determine the range

Calculate the elevation correction needed for that range and apply that correction

Determine  the wind speed

Calculate the effect the wind will have, using the formula provided, and apply that correction

Make the shot before the conditions change

Your goal should be to be able to do these calculations in the field from memory and thus make hits quickly. Situations can change quickly and you have a huge advantage if you can do the mental calculations without digging for calculators, note cards, pens, papers, or palm pilots.

Jeff Hoffman has been a law enforcement sniper since 1989. He is a Reserve Deputy in Pennington County SD, and is Sniper Team Leader of the Pennington County/Rapid City SRT.  He is President and co-owner of Black Hills Ammunition, Inc.

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