Moving Target Engagement

Stationary paper targets have a serious drawback for the shooter who wants to become a complete rifleman.  They are stationary (please don’t be jealous of my insightful pearls of wisdom).  “Real world” targets, whether in the hunting field or the battlefield have a tendency to move.

Generally there are two broad categories for how things move, predictable and unpredictable.  A predictable target is generally one that is moving to a destination.  An unpredictable target moves because it is engaged in an activity, grazing, can’t sit still, etc…

The unpredictable target will usually move for a period of time, then stop, followed by more movement.  For this type of target you can usually wait until it stops.  I have heard this referred to as “patterning”.  I recommend dry firing at chickens’ heads to pick this up.  Just choose a target from one of your chickens as they meander around the chicken run and try to get a head shot from a decent distance.  The chicken will stop momentarily for eating or drinking.  You have to be quick because it won’t stay there long, and their head move very erratically.  Don’t worry, we’re not violating any safety rules, because if you shot it you could eat it.  Yummy.

If you don’t have any chickens…  I’m guessing you probably have a TV. In that case I would recommend placing a piece of armored steep behind your TV.  Then shoot your TV and buy some chickens (reader assumes all risk associated with following stupid advice).

For shooting at predictable targets, you will be solving the following problem: “How far will the target move in the time it takes my bullet to reach it?”  That really is the essence of the problem.  Just remember that and the numbers won’t be as confusing.  You’ll need to solve this problem ahead of time, because it involves math.  You don’t want to be doing math when it’s time to shoot.  As Tuco said in “The Good, The Bad and The Ugly”: “When you have to shoot- shoot, don’t do math.” To work this out you’ll need:

1. Access to a ballistics program that can give you time of flight for your load at any given distance.
2. A way to estimate your distance to target.
3. A way to estimate your target speed.
4. A calculator.

For item 1 I like to use the Berger Bullets Ballistics Program.  There are several ways to satisfy the range estimation factor, so I’ll gloss over that for now.  As for estimating target speed, you’ll probably need to do some research on your target.  Is it a deer, a coyote, an elk? How fast do they walk? How fast do they run?

On to the math.  Most people think of most moving objects in miles per hour.  I know I do, so I tend not to fight that urge.  Let’s say we have a target that moves at 5 mph and the movement is perfectly lateral to us.  Our bullet speed is measured in feet per second.  We need to compare apples to apples, so let’s convert the target’s speed in MPH to FPS.  The conversion from MPH to FPS is MPH(1.467).  For our example of 5 MPH, that would be 5(1.467) = 7.335 FPS.

Now that you know how fast the target is moving, you need to figure out how far it will move in the time it takes your bullet to reach it.  To accomplish this you need to know your distance, and the corresponding time of flight (TOF).  The TOF is the important number we need, but it’s dependent on the distance.  Let’s say the target is at an even 200 yards.  With my imaginary 155 grain Nosler Custom Competition bullet going 3000 FPS my time of flight will be around 0.2149 seconds (as predicted by the Berger Ballistics program).

To figure out how far my target will travel in the amount of time my bullet takes to reach it, we’ll use the old D = R*T.  That would be D = 7.335*0.2149. D = 1.576 with the value being feet.

Having the lead value in feet is okay, but it’s not going to be a very precise way to place a shot at 200 yards.  Instead, let’s say you have one of those really cool mil reticles that enhances your ability to utilize your shooting platform to the utmost (lucky!!!).  Then we’ll have to convert that value to mils.  Since we have been thinking in feet so far, but shooters tend to think in yards, we have to remember two things: 1.) That a mil equals 1/1000 of the distance to target, and, 2.) There are 3 feet in a yard.  That means that the denominator in our formula will be Yards(.003). That would be 200(.003) = 0.6

Let’s finish out the formula.  We’re still converting feet to mils at our distance of 200 yards.  That is 1.576/0.6 = 2.6 mils that the target will travel in the time it takes our bullet to reach it.  That makes your lead, on a 5 MPH target at a distance of 200 yards, 2.6 mils.

The entire formula calculate your lead in mils is:

(mph)(1.467)(TOF) = Lead in mils
Yards(.003)

Where:
mph= target speed in miles per hour
TOF= bullet time of flight
Yards= distance to target in yards

This assumes that your target is traveling at a 90 degree angle to the flight of your bullet   I encourage you to give this a try at the range from a known distance with a moving target of a known speed.  I was just as skeptical as you probably are, but it works.

Remember that you need to do the math ahead of time.  You can plug the formula into a spreadsheet.  Then you can make a quick reference chart.  Here’s what mine for my .308 looks like:

Mover Chart
It would help a lot to have something general committed to memory so you don’t need to consult a chart before you fire.  The chickens probably won’t wait for you.  Notice that the lead values for any given speed seem to move up rather gently and regularly as the distance increases.  This is helpful.

There are two strategies you can use to hit your moving target, “trapping” and “tracking”.

Tracking involves moving your rifle along with the target while attempting to maintain your point of aim and pressing off a shot.  I think that this works better when your target is closer or appears to be moving somewhat quickly relative to you.  A 3 MPH target at 100 yard appears to be moving quickly to me.  This seems to require a more dynamic technique, which is what tracking is.

Trapping involves waiting for your target to cross your point of aim, then breaking the shot at the precise moment that it arrives at your correct lead.  This could allow you to get “set” a little better.  The drawback is that if the target is moving quickly, you’ll have to press the trigger quickly.  This could be detrimental to your accuracy.

I mentioned before that the formula I referenced above gives a lead for a “full value” moving target, i.e., one that is moving at exactly 90° to your bullet’s flight path.  What if the target is moving at a different angle?  Let’s take it step by step.  A target moving at 90° is a full value lead.  A target moving at 0° would have no lead (although technically the distance of the target will change).  Obviously, a target moving at an oblique angle will have a lead value more than zero, and less than 100%.

To figure out the lead for a target moving at an oblique angle takes a bunch more math, multiplying the full value lead by the sine of the angle.  I did this in excel and had to convert the angle from degrees to radians to get it to work.  It was a pain.  Here’s a relevant question.  How accurately can you determine the angle that your target is moving under stress and time?  Here’s another.  How well will you be able to remember the correct value and perform the calculation?  Have we even considered what a breeze is going to do here (are you dizzy yet?)?  With that in mind, here is probably too much information:

Angle of Target Movement           Multiply the full lead by:

75°                                                    .97

60°                                                    .87

45°                                                    .71

30°                                                    .50

15°                                                    .26

This is mostly just theoretical information so you can get an idea of how it works.  I’m thinking that the most you can reasonably expect yourself to keep track of is a full lead value for the most likely average speed of your target.  If the speed increases, you might add a little lead.  If the speed appears to double, double the lead.  If the angle is significant, you might cut the lead in half.  If the angle is not so significant, you might just shave a little off.

The best way to learn to handle moving targets is to shoot moving targets.  Theory is fine, but rounds downrange is where it’s at.  So get out there.

 

 

 

 

 

 

 

3 thoughts on “Moving Target Engagement

  1. What is the formula for a moving target in meters? I noticed that your denominator was in yards. Does this mean that the whole formula will change if its in M? Thank you.

    • Peiter,

      If all the other information is the same in the numerator, you can substitute “meters(0.00328) in the denominator. If you’re using something other than miles per hour and feet per second, you’ll need an entirely different formula.

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