Mil-Dots Made East Part 2

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″.

Screen Shot 2014-03-19 at 10.48.28 PMThink 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.

movingdeer
Point of aim for a deer walking 3 mph at 100 yards.  The red starburst is the intended point of impact.

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.

6mildotlead
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.

Screen Shot 2014-03-21 at 8.11.34 AMAll leads are in inches.  As you can see, the actual lead required is very close to the simple lead described in this post.  

My next post on mil-dots, part 3, will focus on using mil-dots to compensate for wind.

Mil-Dots Made Easy

Mil-dot scope reticles are very common these days, and you can enjoy the benefits of a mil-dot scope on your favorite tactical tack-driver as well as your hunting rifle.  If you Google “mil-dot” you will find more information than you can imagine (and maybe more than you want to know!) on the differences between Army and Marine-style mil-dots, what a mil is, and how to use them.  Looking at the images below, no wonder mil-dots seem so perplexing!

mildotsArmy and Marine-style mil-dots can seem overwhelmingly complex at first, but the fact is both are easy to use for weekend shooters at the range and while hunting game like whitetail deer.

Besides the fact that they look cool, why should the average Joe use a mil-dot reticle in the first place?  Two things: range estimation and adjusting aim for wind and/or a moving target.

Range estimation with mil-dots is just that, an estimate.  All of the fractions and decimals you see in the pictures above are important if you are sniping in Afghanistan at 1,000 yards, but if you are simply trying to determine whether a deer is 250 yards away or 400 yards away, those minor details aren’t as important.  However, the farther away your target is, the more precise you need to be with mil-dots.  Hence the detailed examples above with fractions.

Here’s the simple formula for mil-dot range estimation:

formula

The “trick,” if you want to call it that, is to estimate the height of your target in the same units  you will be using for distance, in this case yards.  If you want the distance to the target in meters, estimate its height in meters.  If you want he range in inches, estimate the height in inches.

deerinscope

So, how far away is this deer?  Well, whitetail deer are about 18″ tall from shoulder to back, and 18″ equals 0.5 yard.  The distance from shoulder to back of the buck is approximately 5 mils.  Plugging that into the equation yields:

Range = (0.5 yards * 1,000) / 5 = 100 yards.

Range = (18 inches * 1,000) / 5 = 3,600 inches

Not too difficult.  Next time you go to the range, take a yardstick and place it at 100 yards. The stick should extend from the top mil-dot to the bottom-mil-dot of your reticle.  Click here for a printable targets and tables that can be used for range estimation.

There is one other very important thing to know about mil-dot scopes.  If your reticle does NOT change size as you zoom your scope, make sure it is at maximum zoom when ranging. This is critical!  Technically, this type of reticle is a Second Focal Plane reticle or SFP reticle.  Most consumer mil-dot scopes are SFP.  So, the zoom setting should be 9 on the common 3-9 scope when ranging because SFP mil-dot scopes are always calibrated at maximum zoom.

If your reticle changes size as you zoom, you have a First Focal Plane reticle or FFP reticle. In this case, the zoom level of your scope does not matter.  More expensive military scopes have FFP reticles.

Screen Shot 2014-03-19 at 10.54.06 PM
What happens to the sight picture with a FFP reticle when zooming.

At longer ranges, estimating your target’s height and number of mils becomes more important.  For example, if your target is 6′ tall and roughly 2.5 mils, the range is:

Range = (2 yards * 1,000) / 2.5 = 800 yards

If the same target is more accurately milled at 2.75 versus 2.5, the actual range is:

Range = (2 yards * 1,000) / 2.75 = 727 yards

At that distance, holdover for 727 and 800 yards is vastly different.  For a standard 150 grain .308 Winchester round, the bullet will drop about 43″ from 727 to 800 yards!  Now you can see why military snipers must be accurate when measuring with mils.  If you want to see the ballistics calculation for that 43″ drop, click here.

Practice ranging with your mil-dot scope each time you shoot with it.  Before too long you will be able to estimate distances with relative ease as you get used to gauging your target’s height in yards and doing a little mental math.

Stay tuned and learn how to lead a moving target and adjust for wind with mil-dots in my next blog post.