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.

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

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) =

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) * 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)

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:

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 |

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