In my last blog post, I demonstrated how to use mil-dots to range distance. The objective of this post is to provide a simple method for the average Joe to hit a moving target with the assistance of mil-dots. Unless you like math, the calculations can seem complicated, so we’ll leave the complicated math to other websites like this one.
However, some basic math is required up front to help you understand the application part, and that’s critical. Don’t worry though, you won’t need to remember the math part when you’re shooting with this simplified technique.
The measured distance between mil-dots at 100 yards with a second focal plane scope at maximum zoom is 3.6″. Remember from my last post that most consumer-level mil-dot scopes are second focal plane. For a first focal plane reticle, the distance is 3.6″ no matter what the zoom. As you can see in the picture below, the measured distance between mil-dots expands proportionately with distance. Therefore, the distance between mil-dots at 200 yards is 2 * 3.6″ = 7.2″ and at 300 yards is 3 * 3.6″ = 10.8″.
Think of a “mil” as a small angle that widens to 3.6″ at 100 yards. As the angle expands downrange, width increases proportionately. When you lead a target 1-mil at 100 yards, you are leading by 3.6″ When you lead a target 1-mil at 300 yards, you are leading the target by 10.8″.
Most sporting rifle bullets leave the barrel with a muzzle velocity between 2,600 and 2,800 feet per second. That’s important because muzzle velocity is part of the calculation to determine how long it takes the bullet to fly 100, 200, 300 yards and beyond. Military studies show that the probability of hitting a moving target beyond 400 yards is relatively poor (less than 75% for trained snipers), and snipers are discouraged from shooting moving targets beyond that distance (Source: The Ultimate Sniper, Maj. John L. Plaster). Since hunting shots at that distance in WV are few and far between, we will concentrate on distances out to 300 yards.
At 2,700 feet per second (fps), a .30-caliber bullet takes 0.12 seconds to travel 100 yards, 0.24 seconds to 200 yards, and 0.37 seconds to 300 yards. Click here to see the ballistics table with these calculated values. A person walking briskly travels around 3 mph. You have seen thousands of people walking at that speed in your life, so it should be relatively easy for you to gauge when your target is moving at that speed. If you convert 3 mph to inches per second, you get 53 in/s. Since it takes 0.12 seconds for the bullet to travel 100 yards, the target moves 53 in/s * 0.12 s = 6.3″ during the bullet’s flight time. (Remember the equation Distance = Rate * Time from Middle School math class?) This target requires a 6.3″ lead at 100 yards. That’s within 1″ of the measured distance between 2 mil-dots at 100 yards which is 7.2″ (2 * 3.6″ = 7.2″).
The exact lead is 1.75 mil-dots (6.3″ divided by 3.6″), but 2 mil-dots is close enough for hunting purposes because the extra 0.25 mil is less than 1 inch at 100 yards.
Here is the simple method:
- Lead your target 2 mil-dots when the target is moving at the pace of a human’s fast walk.
- Double that to 4 mil-dots if it’s moving at human jogging speed.
- If the target is moving at the speed of a running man (~10 mph), lead 6 mil-dots.
- In-between those speeds, use 1, 3, or 5 mil-dots.
Granted, there is no 6th mil-dot from the cross-hair, so you’ll need to estimate that, but at least you have a reference point. This method works no matter what distance your target is out to about 500 yards because bullet velocity is relatively constant to that distance.
The Burris G2B mil-dot reticle, available in their MTAC line of optics, is my favorite style of mil-dot because of the 1/2 mil hash-marks. Learn more about the G2B reticle here. The red line shows the approximate hold point for a 6-mil-dot lead.
The table below shows how close the leads from the simple method are to the exact leads which would require a calculator or printed table for reference. As you can see, out to 300 yards, the simple method is very close to the calculated lead. Even out to 500 yards, the simple method is pretty darn close.
My next post on mil-dots, part 3, will focus on using mil-dots to compensate for wind.