Previously, I discussed a way to simplify some of the exterior ballistic considerations police snipers need. All too often, we get so enamored with the scientific minutia, the process becomes more complicated than necessary for the real world.
Most snipers have developed a personal range card derived from the detailed log book they keep of every shot fired through their rifle. Some go even further and use a ballistics “app” on their smartphone to calculate their shots with truly surgical precision. Such precision is all well and good — if you still maintain the skills necessary to make the shot without your log book, range card, or smartphone app.
Since any police operation can fall prey to Sergeant Murphy’s Law, law enforcement snipers must be able to deliver the goods even when their range card gets lost while crawling into position and their smartphone battery dies. A sniper must have basic elevation and windage knowledge committed to memory, and some “KISS” memory aids can help.
For the “standard” police sniper rifle/load, a .308 Winchester round launching a 168-grain Open Tip Match (OTM) bullet at about 2650 feet-per-second*, there are some very basic techniques that will allow you to work out the corrections needed for body shots out to 600 yards (well beyond normal police engagement range).
The trajectory adjustments necessary are very easy to remember. Assuming a 100-yard zero, your corrections for ranges out to 600 yards are: 2 – 3 – 3 – 4 – 4.
Adding 2 Minutes-of-Angle (MOA) of elevation will put you on at 200 yards. Adding another 3 MOA (a total of 5 MOA of elevation adjustment) will put you on at 300 yards.
Using my simple memorization chart, the total elevation changes necessary for 200 through 600 yards equal 2/5/8/12/16 MOA. Check this with your personal log or a ballistics program and you will see the values fall within ½ MOA and in some cases within ¼ MOA (good enough for body shots). For intermediate distances, split the difference between the hundred-yard values.
If you work at a high-elevation locale, say more than 3,000 feet above sea level, your bullets will drop less, requiring less correction.
Range Minus One windage Formula
My friend Jeff Hoffman, the honcho of Black Hills Ammunition and still an active reserve officer/sniper, has developed a similar rule of thumb for windage for .308 Winchester 168/175 grain OTM loads. To summarize his full article on the topic here, your windage corrections for a full-value 10 mile-per-hour wind are calculated using a “Range Minus One” formula.
For example, for a 200-yard shot in a 10-mph full-value wind (90 degrees left/right), the necessary correction is 1 MOA. Two (hundreds of yards) minus one = 1 MOA correction.
A 300 yard shot will require 2 MOA correction (3-1=2).
Again, this formula produces body-shot tolerances, but it is accurate to within ½ MOA out to very long police distances. Different wind directions will alter this by fractions you should already know: a half-value wind needs one-half the correction.
Marine Windage Formula
An alternative windage formula I have used for years was taught to me as the “Marine formula.” With the Marine formula you must pre-calculate a windage “factor” for your given load.
I’ll give you the windage factor for the standard 168 OTM load: 12. The formula goes like this: Multiply the hundreds of yards by the wind speed in mph, then divide that value by the wind factor (12 for our 168gr load). The result of the formula is the MOA value needed for the wind correction.
So, a 300 yard shot in a 10mph full-value wind goes like this: 3x10=30 … 30/12=2.5 MOA of correction.
Although it requires a bit more mental gymnastics, I find this formula to be a little more accurate than Jeff Hoffman’s Range Minus One formula. Another advantage is that you can figure out the Marine formula windage factor for other loads. For example, my long-range deer hunting rifle, which generates more velocity with a more efficient bullet, has a wind factor of 20.
By memorizing these simple elevation/windage rules of thumb, you are prepared for a worst-case scenario when all of your carefully prepared records or hi-tech tools aren’t available.
*The generic values are also “close enough” for the US 7.62mm NATO M118LR round using a 175 grain OTM.