Rifle Marksmanship

Shooting the Mover Stages

This is a refinement of an article I had originally written and posted over at the Maryland Shooters "Competitive Shooting" forum. It was intended to assist shooters new to moving targets and posted in preparation of an upcoming event.


First, there is no real mystery to hitting the movers. All we will do, regardless of the mover's current position, is shoot where the mover will be when the bullet arrives. If this is properly executed, we will have first round hits. I realize that this sounds very simple, but it can be quite challenging and entails the solving of several firing solutions to arrive at the desired effect. As distances increase, so do the challenges, because we have the environmental and trajectory parameters that will become increasingly more influential.


Necessary Ballistics Considerations

To more easily discuss this, we will need a ballistic example. For simplicity, we'll use the .308, a popular and quite commonly encountered cartridge in practical and tactical style competitions. We'll use the Sierra 175 grain BTHP bullet at 2,600 feet per second for our ammunition, which duplicates the Federal Gold Medal Match (FGMM) ammo ballistics and some military loadings from the average 24 to 26" rifle.

While many shooters use the Sierra 168 grain BTHP loading in Black Hills Match or Federal Gold Medal Match loadings, which usually shoots extremely well, this bullet does not exhibit the dependable long range performance we often need for all around use.

In all situations in which we use "drop", "wind deflection" and "time of flight", bear in mind that these values will vary with the exact caliber and load used. There are too many variables that will influence YOUR results, so the information presented here is an approximation. You will need to know what your particular rig will do, and tailor the values accordingly. It will be necessary to know the exact values of the parameters listed above to be successful at longer ranges, and all of these can be (more or less) predicted by several ballistic software available.

I use Sierra I-5 software for my own ballistic calculations, and I find it to be a very useful product. ExBal is another useful and popular ballistic software that offers the added utilities of offering Palm (field portable) versions, as well as exporting to Excel. Once the ExBal data is exported to Excel, custom ballistic tables can be generated and printed by customizing the parameters displayed. JBM is yet another effective ballistics software that has the advantage of being available in an online (free) version.

Because of the extended ranges we'll encounter, we should probably discuss some aspects of basic ballistics first.

Within about 600 yards, our atmospheric density is normally not very important to our calculations. We can experience quite a bit of variation in air density before our point of impact is influenced enough to take us off most targets. It takes a distant back seat to many other variables, such as field positions and range estimation.

Beyond 600 yards, we'll need to consider the atmosphere and it's impact upon our bullet's flight with increasing concern as we move back. Air density varies with the barometric pressure, temperature and physical altitude, and has a definite measurable effect on bullet performance. At 1,000 yards, it is entirely possible to see two FEET, or more, difference in drop, due only to air density. We will usually use the aeronautic term "density altitude" to express air density. Density altitude is very useful, because it combines the effects of the various factors into one easily digested number. Your density altitude is the apparent physical altitude one would be at, were all other conditions at "standard". As one increases temperature or physical altitude, this number also increases, and indicates decreasing air density, or, lessening resistance to the bullet's travel. As the barometer increases, this number decreases, and indicates an increase in air density, and increased resistance to the bullet's travel.

All of the ballistic software packages will use air density to calculate ballistic predictions and some will aloow you to change the reference used. I use "Army Standard Metro", usually the default settings, and then change the physical altitude setting to calculate air density changes. For simplicity, I would suggest using a "zero" for our physical altitude and then calculating changes from there. There are other methods that will work.

Our ballistic coefficient ("BC") is our next important consideration, and a large part of why we select the 175 BTHP for long range work in a .308. The ballistic coefficient is the numerical value used to express how easily the bullet slips through the air, and thus how much it is affected by friction. Friction and speed will determine our time of flight to any given point, which, in turn, determines our drop and drift.

Once we have our ballistic parameters figured out, we can generate ballistic tables for handy reference in the field. It is handy to have the resolution of our tables at 25 yard increments, but this can become bulky and cluttered if we go to very long ranges, so we can use 50 yard increments with a decent degree of accuracy if need be. Bear in mind that between 950 and 1,000 yards, our example .308 (with the 175 grain bullet at 2,600 fps muzzle velocity) will drop about 3 feet, so it will be necessary to calculate intermediate ranges when they are encountered.

Another factor is the ammunition temperature. Density Altitude only addresses air temperature and the changes in air desnity that result, but the ammunition temperature can alos have a very pronounced effect on trajectory.

Now that we have our rifle zeroed in at 100 yards, and some suitable ballistics tables printed, we can move forward. Ideally, you would prove your ballistics tables out with field data from firing at the various distances.

The first thing we'll need to do when we are on the range and getting ready to shoot is determine distance and correct for our trajectory.

Our distance will sometimes be known, sometimes estimated, and the more accurate our value here, the more accurately we can calculate our drop and drift.

While it is often possible to use holdovers to shoot static targets successfully, the lateral hold required for moving targets will already require a hold-off in the direction of movement, and if we must hold over/under too, our impact reference will be inexact and difficult to maintain. For this reason, it is strongly suggested that one dials elevation.

Next, we will compensate for the wind. This too becomes increasingly important as we move back, and even a small amount of wind can have a large effect. Learning to read wind indicators, evaluate wind drift effects over the course and providing yourself accurate compensation is a whole 'nuther subject, so suffice it to simply say here that you will want to offset the wind. While some shooters will hold off for wind, rather than dial, I would again suggest dialing our wind on. This is because we are going to hold our target lead, and if we set ourselves up to hold wind too, we can easily compound a mistake. Further, when we get the chance to correct after a miss, it will be far easier if we started out with our crosshair (point of aim) being the same as our point of impact.


Target Movement

Now, we are dialed on for range, have compensated for wind, and can (assumably) hit a static target. We only need to evaluate the moving target and how far it will move while the bullet is traveling. How far the target will move relative to the shooter is dependent on how fast it is moving, and at what angle to the line of fire it is moving in.

To correctly compensate for target movement, we'll need to know a few things. We need to know the target's speed, we need to know our bullet's time of flight to that location, and, knowing these things, we can calculate how far the target will move before the bullet arrives.

The easy part can be done first, we can estimate our time of flight from our ballistic software. If our target is at 300 yards, our software says our example .308 will need 0.386 seconds to get there. If our target is at 800 yards, we are now looking at 1.267 seconds as a time of flight. 1,000 yards will take 1.73 seconds.

The angle of travel is very important. Obviously, a target moving at right angles to the shooter will require maximum (full value) lead, while a target moving straight away will require no horizontal lead at all. We can handle intermediate angles of travel with the use of the cosine, much like we compensate for wind at odd angles to the line of fire. For our purposes of introduction here, we can assume a target traveling at right angles to the line of fire, and will thus require a full value lead.

Now, our target speed must be judged. Target speed is literally infinitely variable, and there are guidelines that can help one estimate target speed. Since we know that our targets used in the "Mover" stage of many tactical matches will be hand carried (on long sticks), we now have a more narrow range of speeds we can work within. For example, average walking speed is around 3 MPH. Average running speed can be as much as 7 to 8 MPH.

We must also remember the trick of the eye that as the subject is viewed from farther away, it will seem to move slower. For this reason, all moving targets must be compared with their immediate surroundings to be able to estimate their speed.

If we can pick two objects that are a known distance apart, like two vertical (target marker) posts six feet apart, we can time how long it takes the target to travel the six feet and estimate speed in FPS from that reference. We can also use out mil dot or MOA reticle to provide a reference speed. This is handy, since we will need to know the target speed in "units per second" to use with our time of flight that we have calculated in seconds. Otherwise, we will need to reduce target speed to FPS via calculations.

To calculate from MPH, we'll convert "miles" to "feet", and 1 mile per hour becomes 5,280 feet per hour. To reduce this to feet per second, we can divide 5,280 by 60 (FPM), then by 60 again (FPS). From this, we see that 1 MPH is equal to 1.467 FPS, or, in one second, the target will move 1.467 feet.

We can condense this formula for field expedience by doing some of the math ahead of time and making it a single factor. We can divide the feet in a mile by 60 to get the FPM per MPH, divide this again by 60 to get the FPS per MPH. The formula for our conversion factor would look like this: "((5,280/60)/60)" and will result in the factor "1.46666".

If we take an average walking speed of 3 MPH and run our calcs, we now know that this is about 4.4 FPS (3 x 1.4666 = 4.4). If we are presented with an angle of less than 90o to the line of fire, we would now apply our cosine correction to provide an adjusted apparent speed. Otherwise (like now), we will use a full value lead.

Using an average walking speed of 4.4 FPS (which just happens to be equal to 1.36 seconds to move 6 feet, in case you have something out there that is about 6 feet to measure with), we can multiply this by our time of flight to find our estimated lead.

At 300 yards, our time of flight is 0.386. Using our .308 example, our time of flight (0.386) time the speed in FPS (4.4) will equal our required lead (1.7 feet).

Using our same walking speed of 3 MPH~4.4FPS, but now shooting from 800 yards, our lead increases significantly. Our new time of flight is 1.27 seconds, so, 1.27 x 4.4 = 5.6 feet, and so we will use 5.6 feet of lead.

Not intended to discourage, but as a necessary reality check, it is important to note just how difficult consistent results are on movers, and just how little error in any given step in our calculations can lead to a complete miss. For example, instead of the prescribed 3 MPH, what if our pit crew has had a LOT of coffee this morning and is actually moving closer to 4 MPH?

At only 300 yards: If, instead of 3 MPH, the target moves at 4 MPH x 1.46666 = 5.9 FPS x 0.386 = 2.28 feet of lead. One mile per hour variation results in .58 feet of error, or, a 7" miss. At 800 yards, this same 1MPH error produces 2.5 feet of error.

Needless to say, there is going to be some talent and "feel" required to be consistently successful on movers at anything but rather close ranges.

Holding the lead and maintaining the proper distance out in front of the target can be done in one of two ways. We can estimate this distance, using something downrange to give us an approximate value. For example, some might find it quite interesting that a B-27 target is about 24" wide, and just a little less than 24" lead (20.4") is required at 300 yards for our 3 MPH example. Unfortunately, this doesn't always work as well at that.

The other, more precise method is to measure, using your scope reticle. Most shooters inclined to shoot these match are using a mil dot scope, so we'll use that example. As we know, the mil is a unit of angular measurement, equal to 3.5 MOA, that remains constant from our perspective behind the scope, but provides varying subtension as the range varies. To use our mil dot reticle to measure our lead, we need to know what distance it subtends at the given range.

At 300 yards, 1 MOA is approximately equal to 3.14", so 1 mil will be worth 11" at 300 yards. If we need 1.7 feet (20.4") of lead, this is 20.4" divided by 11"/mil, and equal to 1.85 mils. In practice, we would just use our second mil dot and call it a day.

At 800 yards, 1 mil subtends 29.32". If our target requires 5.6 feet of lead, we see that we will need to use 2.3 mils of lead.


Executing The Lead And The Shot

Now that we have figured out how to calculate and measure our leads, we now need to break the mold of holding our rifles motionless against a motionless targets, and figure out how to adapt ourselves to following a mover.

There are three basic methods in use for shooting moving targets with a rifle: "Ambush", "Sustained Lead" and "Swing Through". We can discuss the techniques, pros and cons to the various methods and decide which one will best suit our purpose.

The "ambush" method refers to putting the stationary target in place where the target is expected to appear, and firing when the target reaches the point where the lead has been established. Because the gun is held stationary, we can shoot from the bipod and don't have to change our "old faithful" (static) method of shooting longer range targets. The single biggest problem with this approach is that the split-second timing will often cause one to jerk the trigger, and even when we get the lead and timing right, our bullet may still go astray due to a bad trigger pull. The second drawback to this method is again related to the required split-second timing, and that any delay or error in reaction time can and will substantially modify the lead you end up with. It is extremely difficult to hit a moving target with a stopped gun, and any experienced shotgunner will tell you that stopping your swing is the best way to miss a bird, even when everything else is right. This method often provides good results with new shooters because the fluidity of motion used with other methods can be difficult to achieve at the beginning stages. It is easier to teach and learn when time is limited. Due to it's drawbacks over the long term, it is used mainly to introduce shooters to movers and when they become accustomed to shooting the moving target stages, they are transitioned over to the sustained lead or swing-through methods.

The "sustained lead" method is when the target lead is held in front of the advancing target long enough to match speeds, then the trigger squeezed as one maintains the correct lead. This is a more desirable approach, and rather easy to apply if the target moves at a steady speed and is expected to continue in it's current line of travel. The downside of this method is that the tendency to stop the gun as the trigger is pulled is very strong. Again, stopping one's swing is an almost guaranteed way to shoot behind the target. The other drawback here, and one it shares with the ambush method, is that the target must be moving steadily, and in a single direction long enough to apply this sustained tracking. In the case of pass shooting high birds, it's not a bad way to go. The high passing bird is on a certain track, flying at a certain speed, and the sustained lead method lends itself well to this sort of shooting. For shooting something traveling along the ground, with the tendency and/or ability to abruptly change direction and/or vary speeds, it becomes less effective.

The "swing through" method is when the target is pursued from behind, the gun/reticle moved past it, and when the necessary lead distance is achieved, the trigger squeezed. This is my personal favorite for all sorts of shooting. Because the gun is accelerated from behind the target, swung through and the trigger squeezed all in one fluid motion, the tendency to stop the swing or to jerk the trigger is almost non-existent. I begin to apply pressure to the trigger as the reticle moves through the target, and complete the pull at the instant the lead becomes right. Because it is quickly and smoothly executed, the target has much less opportunity to stop, vary speed or change direction than the sustained lead method.

If a rest is needed, both the sustained lead and swing through methods are best accomplished shooting over a pack or other smooth object that will allow the gun to move freely. It is also quite comfortably done from slung prone or slung sitting, if the extent of target motion does not cause you to break your position. If the target is moving that fast across your field of fire, it is probably close enough to hit without support.

Some dry fire practice can go a long way toward smoothing out whatever system you decide to begin with. Following birds in flight, pulling ahead and either maintaining a nominal lead or swinging through and executing your trigger pull is an excellent way to get started and will give you a good feel for what to expect when firing a moving rifle.

Hopefully, those intending to shoot some of the matches will find this helpful with the mover stages. The thing to remember is that consistently hitting movers is either the pinnacle of long range precision shooting, or, the pinnacle of luck, and not to be discouraged if success is not immediately forthcoming. There are many precision shooters who have no idea where to start with the challenge of movers, attending matches is a great opportunity to just go out and have fun doing something besides shooting at stationary paper.




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