Advanced Marksmanship Lead Estimation

[bribassguy]

I took a kestrel class and learned about the lead estimation function. You basically are using a stop watch to find lead. I don't have a fancy kestrel so I wanted to see if I could do the math long hand.
I am also not a great judge of speed… are the movers at 2 or 2.5 mph at 600??? I was guessing at speed and thought if I had time I would see if I could measure it give standard stuff in my kit (Range Card, Reticle, Chrono Watch). I wanted a quick lead calculation based on time of flight and observed time to travel 10 mils in reticle at a known distance.


I think that the math is right but I was hoping someone could check me... or just share this method.

Step 1.
I used a ballistics app to get ToF and added it as a column to my range card I keep in my data book.

Step 2.
Estimate Target Speed... Speed is Distance over Time so I used the WORM method to work out how many feet a target would travel across 10 mils at a given distance then timed target to get speed. I used fps because my time of flight is in seconds and it made the conversions easier.

Target speed (fps) = Width of travel (ft) / Time of Travel (sec)

Width of travel (ft) = Mil of Travel * Dist to Target (yd) * 1/1000 * 3 (ft/yd)

Target speed (fps) = ((Mil of Travel * Dist to Target (yd) * 1/1000 * 3 (ft/yd) )) / Time of Travel (sec)

Step 3.
Lead is basically the distance your target travels in the time it takes the bullet to get there. To accomplish this you need to know your distance, and the corresponding time of flight (TOF) and target speed from above.

Lead (mrad) = TOF (fps) * Target Speed (fps) / Dist to Target (yd) * 3 (ft / yd) * 1/1000 (mil/yd)

Sub in Target Speed
Lead (mrad) = TOF (fps) * Mil of Travel * Dist to Target (yd) * 1/1000 * 3 (ft/yd) )) Time of Travel (sec)
/ Time of Travel (sec) * Dist to Target (yd) * 3 (ft / yd) * 1/1000 (mil/yd)

Simplify: This gets a whole heap easier so long as you are observing and shooting from the same distance. You can drop out a lot of the conversions and use just 3 inputs.

Lead (mrad) = TOF (fps) * Mil of Travel / Time of Travel (sec)
Proof:
So if I check this out using real data I get pretty close. It’s well with in my shooting error.

Assumptions:
140 ELD @ 2750 Mv @ 600 Yds @ STP = ToF 0.783 (sec)
10 Mil Observed @ 600 yds = ToT 6.1 (sec)
Lead (mrad) = .783 * 10 / 6.1 = 1.28
JBM gives 1.3

I worked up a quick ref chart that give ToT in seconds and does the math.

Example:

	Sec / 10 mil
Dist	8	6	4	3	2	1
600	1.0	1.3	1.9	2.6	3.9	7.7
700	1.2	1.6	2.3	3.1	4.7	9.3

 

[nfoley]

I stopped reading after about the 3rd line, so can't help you with the math. But, I can tell you every time I have shot movers I start with a rough estimate (depending on distance, wind, but usually start with around 0.5-1.5 mil) fire a shot and mark with the reticle if its a miss. Make a quick correction and fire again. Keeping in mind that lead will only work for that direction, may need to change as the mover comes back the other way.
Movers are fun, love shooting them but never got into the math. And I haven't really had a tough time making hits.

 

[Lowlight]

.5 Mil per MPH of the mover... 2MPH = 1 Mil lead. (does not include the wind hold which changes depending on direction)

the problem with formulas is, they only work from the point the bullet leaves the barrel and not before. The reason we need the information before is, that is our personal lock time. We would see people use different leads for the same target and that is because of personal lock time. The time it takes for you to make the decision to fire to the time it takes for you actually press the trigger. That plays a part in it. It's why a guy will come off the line and tell you his lead is 1.5 mils after hitting everything, and then you go and miss everything holding 1.5. The Human Factor. It was pretty common for older people on the line to have a .5 Mil increase in their lead because of this.

That and doing long hand math in the field is a no go to start. If you have to break out a calculator on the line you already lost.

Different apps have different measuring devices to calculate the lead, but usually just know the speed, (and most tell you at a competition) ) then just use .5 Mils or 2MOA per MPH.

The easiest way the FTW Ranch trains hunters is TOF, they track the mover and count, and over that 1 second period, you estimate the distance it moves across the reticle. That 1000 & 1 is your 100 to 700 yard lead within the reticle movement. So figure out the amount of space it covered in 1 second. Works pretty well when you are behind the rifle with no reference beforehand. it will give you the hold, then jump in front and strike.

 

[Sheldon N]

I think I track with what you're saying and do the same thing... just way simpler.

The mover is going to have fixed reference points of some sort. Usually end marker sticks where it's "Don't shoot the mover when it's out of bounds" so you don't destroy equipment. If they're not there you still have the turn around points.

Step 1
Mil the total distance from end-to-end of the travel of the mover.
Super easy to do, get on the gun, or on your Sig Kilo 2200 with a mil reticle in it, or on anything else that will let you mil the target. My Gen II XR reticle has 50 mils of horizontal markers with 5 mil hashes. Just zoom to fit and count the hashes. Worst case you use the 10-15 mils of markers in your scope and just overlap to get the total.

Step 2
Get your stopwatch and time the end to end travel of the mover.
Check both ways if you want, should be the same.

Step 3
Divide Mils/Seconds to get the total number of mils your target moves in one second (ie. mils per second).
Example.... total travel of the target is 42 mils from marker to marker. Stopwatch says 16.5 seconds travel time. 42 / 16.5 = 2.55 mils per second.

Step 4
Multiply your mils per second by your time of flight from your ballistics chart or app to get your lead.
This is a center to center lead, so you need to time the break so that the gun fires when the target is centered on your lead number. Example continued... Your time of flight to the target distance is 0.801... multiply that by 2.55 mils per second. 2.55 x 0.801 = 2.04 mil lead.


This is pretty easy to do in competition barely takes any time to mil the target during stage prep. Timing the target takes only one or two passes. The math is very straightforward to do on your phone, almost doable in your head if you had to. The results are rock solid too. Last comp I was at the 600 yard mover stage brief said they thought it was about 3mph, maybe a bit faster. Nope.... I double checked and used the lead calculated with the above method and cleaned the stage. The mover was actually barely above 2mph.

 

[Kopfjager1]

Ive found a formula that has worked for me thats based off a 2mph FV target speed shooting 175 SMK .308 at 2620fps. Ive only used it out to 800 yds and had no problems with it. It took me a lot of time comparing my data and ballistic computer data (AB), to find a constant that is easy to memorize, or small enough to print on a dope chart along with your other data.

Ive only proven the formula for 2 mph at 800, up to 4 mph at 600, and up to 6mph at 300 while using the tracking method (which for me negates the human factor, again, for me, I cant for the life of me use the ambush method and be accurate). And Ive only used this formula at 27.xx inHg baro, and 29.xx inHg baro, both in the 70-80* temperature range; so not a whole lot of variation. The mover(s) at 800 can probably be considered null because of my ability to estimate the wind speed and direction, all while tracking a target.

If anything this chart can be used as a baseline.. And I realize the "x.05 mRad" is irrelevant, but it makes the formula correct at the faster target speeds. The formula is only correctly estimated for 10 and 12mph up to 500 yds. After 500 yds, its only a close estimate but will most likely miss off of trail edge. The tricky part is you have to add or subtract your wind, if you hold your wind its an even bigger possibility of having the wrong amount to hold. Dialing wind then holding your lead will the most precise, but it comes down to how much time you have.

Range Yds	mRad	2 mph x 1
300	1.35	4 mph x 2
400	1.4	6 mph x 3
500	1.45	8 mph x 4
600	1.5	10 mph x 5
700	1.6	12 mph x 6
800	1.7
900	1.8
1000	1.9

For example Target is at 500 yds (1.45 mRad), target speed is 6 mph( multiply by 3), 1.45 x 3 = 4.35 mRad, round to 4.4 mRad for a full value lead.

 

[SubOptimal]

Something skeet shooters learn very quickly if they are to be any good is lead estimation. They basically work in a different realm than do rifle shooters for two reasons. They are shooting a column of shot at the target and the distances/speeds are quite different. Target distance is short, typically about 16 yards, target is moving anywhere from 45 to 55 mph for machine thrown targets, exposure time is very short (typically about 3 seconds), the angle of the target's flight to the shooter is different at each of the 8 stations and it may be rising or dropping as well. The result is that you cannot ambush a target, you must set the gun on the predicted path of the target, swing through the target and then you have a choice of method. You can swing through the target and attempt to sustain a lead along the predicted path or you can just pull the trigger when your eye tells you you are far enough in front. The most important thing is to keep the gun moving till you see the target either break or fly off to the tune of a "LOST" by the scorer.
This can be confusing to the novice of either sport. I would say that the majority of rifle shooters probably use some form of the ambush method for shooting movers and are going to miss a lot on a skeet field. The majority of skeet shooters are going to miss on a moving rifle target because they have become used to over estimating the lead required on a 2 mph mover. Skeet shot moves at 1250 feet per second and the column at 16-20 yards is a couple of feet long, on station 4, the station that requires the most lead, your barrel will be 3-5 feet in front of the target and you will still get a good break or at least a chip, (chips count in skeet, not so much on steel).

 

[TheGerman]

.5 Mil per MPH of the mover... 2MPH = 1 Mil lead. (does not include the wind hold which changes depending on direction)

the problem with formulas is, they only work from the point the bullet leaves the barrel and not before. The reason we need the information before is, that is our personal lock time. We would see people use different leads for the same target and that is because of personal lock time. The time it takes for you to make the decision to fire to the time it takes for you actually press the trigger. That plays a part in it. It's why a guy will come off the line and tell you his lead is 1.5 mils after hitting everything, and then you go and miss everything holding 1.5. The Human Factor. It was pretty common for older people on the line to have a .5 Mil increase in their lead because of this.

That and doing long hand math in the field is a no go to start. If you have to break out a calculator on the line you already lost.

Different apps have different measuring devices to calculate the lead, but usually just know the speed, (and most tell you at a competition) ) then just use .5 Mils or 2MOA per MPH.

The easiest way the FTW Ranch trains hunters is TOF, they track the mover and count, and over that 1 second period, you estimate the distance it moves across the reticle. That 1000 & 1 is your 100 to 700 yard lead within the reticle movement. So figure out the amount of space it covered in 1 second. Works pretty well when you are behind the rifle with no reference beforehand. it will give you the hold, then jump in front and strike.

The bold part is what I was going to say and have used. I remember this from back in the Bundeswehr in 1999 and always wondered why people wanted to resort to crazy longhand math formulas to try and engage a moving target that 1 - probably wont be moving that fast constantly and/or in the next 20 seconds 2 - will probably be obscured or out of your line of sight by the time you do your math equations and 3 - will probably NOT be moving in a perfect perpendicular path in relation to the gun.

The benefit to this is that you are always just 1-2 seconds away from a new solution should the target change its speed.

Secondly, another thing I remember is getting yelled at for always trying to make shit hard on myself by always trying to engage movers instead of just fucking waiting for the guy to stand still lol but that's a different conversation

 

[Whiskey 2-1]

If given time and opportunity several of the math versions work. One thing Jacob Bynum said once really hit home for me on movers, and while it requires some time with a mover track to pick up, it really is a great way to look at it. This is my version of his idea. When talking about figuring leads, he equated it to playing football or dodgeball or other sports. You don't know the FPS speed of the receiver or the exact angle he is traveling relative to you when you throw the ball to him. You don't do math. You've learned through watching people run, and throwing some balls, how much to lead. This is a factor of how hard you throw, how fast he is running, and in what direction. You can tell if he's walking, jogging, sprinting, etc and know roughly how long the ball will take to get there.

For shooting, we can get a feeling of our time of flight through watching our shots impact after firing at different distances. If you pay attention, you get a good feel for this. You also watch people walk, jog, sprint. Walk next to a mover you have shot before to get an idea of how fast a walk that is. You can then compare the inanimate mover to human movement if you are concerned about fleshy targets. Simply watching a mover in your scope will give a good idea of where to start your lead. Then send one, see splash, and adjust of needed. For example, the RO mover changes speed based on a rheostat (Jacob and Lindy's mood and random crap even during a string of fire) so it's not always the same speed even day to day. I can watch it run when laying down on the line and know when I need to add or subtract 0.2. While that may seen range specific, it's not. It's just having a good internal data book on mover speed related to time of flight. We all do it playing catch.... rifle is no different. You just can't do it in the front yard.

Im not saying don't do the math if you can. I'm just saying it made a lot of sense to me to treat it like throwing a ball instead of plotting a solution.......and LOVE movers.

Doc

 

[bribassguy]

Thanks for the feed back... just to clear things up I am not doing long math at the shooting line I did it once to prove the theory then made a quick reference card. I just wanted to make sure that I could basically ignore distance if I was measuring and shooting the same distance. It's the engineer in me...


I am simply timing the move across 10 mils, then getting lead based on ToF off a card. All the math was done in front of a keyboard.

Example would be a mover at 600 that took 4 seconds to move at 10 mils would get a 1.9 mil lead.

 

[Sheldon N]

Here is a method me and a couple of fellas developed. It's similar to some of the above.

Mrad/sec x TOF = lead (regardless of targets movement angle)

That's it in a nutshell right there. I've been fortunate that all the comps I've been to thus far have allowed for viewing the mover in advance which gets me a bit more accurate estimation. The Sig Kilo rangefinder with the 30 mil wide viewfinder markings is perfect for giving you a wider movement window and then I just stopwatch it to get the mrad/sec. It's simple enough though that you could do it on on the gun in real time like you said.

What always kills me is movers plus dynamically changing wind. I'm working on being able to keep it all straight in my head... 1.1 mil lead, break the trigger left edge regardless of which way the mover is going, spot impacts and refine wind hold, etc.

Oh, and my bonehead move from last competition.... don't shoot the mover outside the cones. Need to remember that the bullet goes where the crosshairs are, not where the lead hold is. Tried to squeak in a shot right before it crossed out of bounds only to realize after the fact that while my lead hold was inside the cones, the actual bullet path and impact was outside. DOH!

 

[Sheldon N]

Yea, with this lead method it's to center of target so I break when crosshairs hairs are just about to hit center of plate.

I can't do the add/subtract thing on the clock... too much math with too much going on under time pressure. I'll dial in wind if it's constant, but that's not always the case. Right now I'm trying to let the lead be its own thing that doesn't get adjusted, then mentally picture the break point as though I were fine tuning the wind hold. Favor left, hold left edge, just off left edge, etc. Ideally if the wind is so strong that I'd be off plate I'll have already dialed in a few clicks on the scope and that way I can just refine the wind by breaking on the windward side of the target rather than center target.

 

[BOLTRIPPER]

my advise ......shoot a lot of skeet, become a good wing shooter,....it will all translate

 

[Gunfighter14e2]

You have a ruler in front of your face. You should be able to count. Think!

 

[mark5pt56]

As usual, LL nailed it, the human factor. I'm like the sloth playing the drawing/guessing game. My reference is 2 mil's for a walker, adjust as needed for slow or fast. A reference for a med walker is 3 mph with a pack on level ground.