AccuracyBallisticsLong Range ShootingMarksmanshipSniper Rifles

Finding your Speed Drop Factor

By: Ted Hoeger (Jack Master)

How long does it take to find our drop data for a target range?  If we need data quickly, most shooters are using some type of paper chart. This chart could be taped to the stock, on a data holder, or arm bar where with a quick glance we can read our data.  What if there is a faster way?  Welcome to the Speed Drop Factor.  Finding and using your Speed Drop Factor will allow you to memorize your drop data to a reasonable distance by remembering one number.

Most rifle calibers have a portion of their bullet flight where the relationship between the drop of the bullet and distance traveled is consistent. A zone where every 100yds of distance is an additional 1mil of elevation. As an example, if our data says 500yds = ~2.5mils, 600 = ~3.5mils, and 700 = ~4.5 mils we can start to see this consistent relationship between distance and come-up. For every 100 yards traveled the come-up is changing 1 mil. As the bullet gets further away and starts to slow down more quickly, this relationship will start to change and will no longer be a constant value, but in the ranges that it works we can use it to our advantage to quickly calculate our come-up.

Before we get too far, let’s understand a couple of limitations for using a Speed Drop Factor.

  1. We must be using a Mil Scope. This does not work in MOA.
  2. Speed drop will only work for a specific range for your rifle, caliber and bullet. We’ll find that range in the steps below.
  3. Some error in the final drop data is expected but we can choose how much error we allow.  This is not a perfect system, but it is reliable if we understand the errors we have allowed.

To find our Speed Drop Factor we need to write out our drop data and do some simple math.  Start by writing out the drop data for each 25-yard increment from 100 to 1000 yards (or more if your caliber is capable).  For each yardage, divide the yardage by 100 and subtract your come-up. [500 yards is (500yds/100) – 2.5mils = 2.5 factor].  Do this for each yardage and start to look for the constancy in this factor.  Below is the excel table I used for my 6.5 Creedmoor with 130 ELDs.

Now that we have the Drop Factor for each yardage, we need to choose which factor works the best for our application over a large range of distances. The Prime factor is the highest factor. In the example below, 2.6 at 600yds is the prime factor. 2.6 is the highest and the center number of the highest. We also must choose how much error we want in the Speed Drop Factor. For each 0.1 under the prime factor (2.5 rather than 2.6), we add 0.1mil error into our firing solution. The more error we allow, the wider range the factor is usable; the less error we allow, the less range the factor is used. 

Speed Drop Chart
Speed Drop Chartg for 6.5 Creedmoor

In this example, if we choose to allow zero error the drop scale factor would be 2.6 (the prime factor) and works from 525yds to 675yds. A drop scale factor of 2.3 will allow 0.3mil error high or low and works from 275yds to 950yds.

The more error we allow in the drop scale factor the more error we will have at the edges of the usable distance, and the center of the usable distance.  At a factor of 2.3 we can see there is 0.3mil error (high) at 275yds and 950yds as well as 0.3mil (low) from 525yds to 675yds.  Depending on your application and caliber you can choose what drop scale factor works the best for you and what ranges you want to use it at.  

For this rifle, I chose a factor of 2.5 to allow for a 0.1 mil error, but I also use this factor from 350yds to 900yds. This gives an error of 0.1mil in the center of the range and up to 0.3 mils at the edges of the range, or about 1MOA. Plus, 2.5 is easy to remember and easy to use in the field.

Steps to find your Speed Drop Factor

  1. Write out the drop data from 100 to 1000+yds by 25yd increments.
  2. Calculate the Speed Drop Factor at each yardage. Divide the yardage by 100 and subtract your come-up. [500 yards is (500yds/100) – 2.5mils = 2.5 factor] 
  3. Find the highest Speed Drop Factor (choose the yardage in the middle of the highest factors)
  4. Choose how much error you will allow at the prime factor. (0.1, 0.2, 0.3, 0.4)
  5. Subtract the allowable error from the prime factor to get your Speed Drop Factor.
  6. Subtract the error you allowed from your Speed Drop Factor to find the shortest and longest range your Speed Drop Factor will work.

Speed Drop Factor can also be calculated with a 5700 Elite Kestrel.  You’ll first need to turn on the Accuracy First ability to find the settings and calculate the factor.

How do we use this Speed Drop Factor?  

There are 3 ways we can use the Speed Drop Factor. The first method is mental math, the second is a BDC reticle and the third is a BCD Turret.

Mental Math

This is doing quick math in our head to get our drop data.  Once we range a target, we quickly divide it by 100 and subtract my Speed Drop Factor.

Range = 660 → 6.6 – 2.5 factor = 4.1mils.

Range = 515 → 5.1 – 2.5 factor = 2.6mils   

To avoid doing math on the clock or in the field we can dial up to the yardage and then dial back down the Speed Drop Factor.  I find this simpler and faster if I am stressed.  For a 720yd target I would dial up to 7.2mils, then back 2mils (5.2) then back another 0.5mils (4.7mils) for my 2.5 factor.  This is how my brain likes to do it, you’ll have to find the way your brain likes to do it.

This is the method I use the most. It’s a quick check whenever I need it. At a match, right before a stage starts, I can ask the range to target and double-check my turret, or when at the range and missing targets I can ask for the target distance and double-check my turret.

BDC Reticle

If your scope is capable of dialing under your zero mark or you can set your zero stop lower, you can dial your scope DOWN your drop scale factor. In my example, I would dial my 10mil per revolution turret down to 7.5 which is 2.5mils below my 100yd zero. Doing this makes the reticle a BDC reticle for the ranges where the drop scale factor works. If a target is at 575 yards, we can hold over 5.7mils. A target that is 800yds is an 8mil holdover. This works for the entire range where the drop scale factor is used.

BDC Reticle
BDC Reticle

BDC Turret

For this application, we slip our 100yd zeroed turret to the Drop Scale Factor. When we range a target, we will dial the target distance with the turret and use the main cross-hair in the reticle (no Holdover). My rifle when zeroed at 100yds will show 2.5mil on the turret because my drop scale factor is 2.5. For a 575yds target, I dial to 5.7mils and use the main crosshair. For 800yds I dial 8mils on the turret and use the main crosshairs. The benefit of this system is getting to use the main stadia line with the best wind holding capabilities as well as more precise dialing and aiming rather than holding over. The downfall to this system is we need to remember our turret is slipped to 2.5mils (setting a zero stop really helps). Our ballistic program can easily be changed if we add a 2.5mil vertical zero offset. This will add 2.5mils to all our data so we can still dial for targets outside the range of the Speed Drop Factor. We could even rewrite our armbar for this offset.

Turrets
Speed Drop using Turrets

For either the BDC reticle or the BDC turret we will need to have some references for our closer targets. For this, I generally use 0.5 mils for 200 and 1.0 mill for 300 yards, it’s very close for most of the calibers I use. For the BDC system, my 100yds zero is a 2.5mil (my drop factor), 200yds is 3.0 mil, 300yds is 3.5 and at 400yds I can start to use the speed drop BDC reticle/turret with the yardage. 

What about environmental changes?  Yes, the environment will change our data, but is it enough change to matter at ranges mostly inside 800yards?  Because this system already has some inherent errors that are likely larger than the environmental effects, the environmental effects can be ignored.  If you would like to know more about how much the environment affects our data read this article: Understanding your Ballistics Calculator Atmospherics

The Speed Drop Factor is a useful thing to keep in your bag of tricks for when you need quick engagements. Although it is not a perfect system it will get you on target quickly with confidence and you only have to remember a couple of numbers.

What is your rifle’s Speed Drop Factor? How much error do you allow and what are your effective range limits?

Here are a couple of additional common-caliber examples. 

Additional Calibers
Additional Calibers
Additional Calibers

Ted Hoeger (Jack Master)

Owner of Sniper's Hide, Bigfoot, The Loch Ness Monster, Aliens, & UFOs

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This could be a game changer. When used with a fatal funnel or a spotter calling range, dialling elevation and making hits would happen extremely quickly with this method.

If you need more precision, keep a correction card with your +- values for fine tuning on smaller targets. A correction card would also help you extend the usable Range of this method.

You could even go one step further and work out the initial speed drop factor for your average density altitude and have another dope correction card for higher/lower density altitudes.

EG
Turret set to average DA SDF.
Slip turret to +- density correction at the start of your shooting session or to the expected DA at location (monitor and adjust as needed)
Range target,
Dial yardage,
Dial +- correction,
Send it.

Very, very cool stuff.
 

RSB4

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I first ran this out at accuracy 1st a few years back. It is a awesome way to engage targets. They did state that it is not a precision tool it’s mainly an RTE tool just like 12” drill or 2/4 mil drill. However it’s a great way to get an initial shot on target
 

st1650

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Depending on your load/distance - it might also work better with range in Meters rather than yards. I used it to make a quick demo to a buddy engaging 2 moa steels at 300, then 400, then 500, no maths - all hits. It's really quick and if you set it up for +/- 0.1 mil instead of the default 0.2 it's pretty accurate and as opposed to a BDC, it will change depending on your load/weather/env - somedays it might be 2.2 instead of 2.0.

Really cool feature, if Strelok would offer it, I'd probably sell my 5700 Elite.
 

Burdy

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Do you need to be somewhere north of 2600 fps for this to work? Not sure what I am doing wrong but my 73g ELDM's from my 13.7" barrel gives some wacky readings on the table. The gun itself has no issues with accuracy out to 800...very consistent. Would like to be able to use a table like this if possible, my MV is 2440 fps @ 60 degrees:

YardsDrop/MillsFactor
15001.5
1750.21.55
2000.41.6
2250.61.65
2500.91.6
2751.11.65
3001.41.6
3251.71.55
35021.5
3752.31.45
4002.61.4
42531.25
4503.31.2
4753.71.05
5004.10.9
5254.50.75
5504.90.6
5755.30.45
6005.80.2
6256.3-0.05
6506.8-0.3
6757.3-0.55
7007.8-0.8
7258.4-1.15
7509-1.5
 

RSB4

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It only works out to a certain distance. Looks like your speed drop number is a 1.5/ 1.6, that’s if you except a .2 shot error so for you it will max out around 400 to 425. Remember it’s going to be different from one caliber to the next
 
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Burdy

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It only works out to a certain distance. Looks like your speed drop number is a 1.5/ 1.6, that’s if you except a .2 shot error so for you it will max out around 400 to 425. Remember it’s going to be different from one caliber to the next
Guess I'll stick with tape and pen for that platform
 

RSB4

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Guess I'll stick with tape and pen for that platform
Lol. It’s really worth running. It’s just another way to engage targets for rapid target engagements. There are other options you can also look at, 12” drill and max point blank, hold over and hold under. Thing to remember they are just a tool with limitations which ever you choose. I do like the fact that I can dial down my speed drop number and make a BDC or dial the speed drop number off the distance and it gives me my D.O.P.E.
 

JustSendit

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Speed drop is most advantageous with a higher BC, fast MV cartridge. 300wm with 190s, 6.5cm with 130s, 260 with 136gr ect.

You can do it with anything but the usable speed drop range I think becomes a little restrictive to get the most out of it. Still a good tool to have nonetheless.

A good example is that 223 73gr chart, if you’re working a +/-.2 error it’s effective between 150 and 400ish. So if you’re engaging in those ranges it’s worthwhile. But for instance 300wm w 190s at my DA calc’d from 250-900.. could be a little off but in that ball park. That’s a nice window for shooting larger targets. By far the biggest advantage is night engagements, where you will not need to reference a dope card or use kestrel backlight. The shooter can do the quick reduction and shoot the target quickly.
 

BLKWLFK9

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    When Ted came and stayed with me, we recorded a podcast and covered the speed drop amongst other things. I am not a numbers guy so naturally, it didnt immediately "click" in my head but i finally somewhat understood. To some people, numbers and formulas just make sense and these things become easy. For others like myself, we have to stare at shit for a long time before the already dim light bulb decides to turn on. I could see this proving very useful in a hunting scenario for sure.
     

    lowlight

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    I think Ted changing the direction of the adjustment is the key factor here,

    By reversing it as he does, you can do both, hold or dial the same way. Yes, you have limitations, but those limitations are within a set of parameters that make sense. Going outside those parameters, in this case, is pretty obvious

    Originally it was meant to work with the confines of the reticle, so you had to Dial Under, and it was sold that way, hence the change from NF to Leupold put a wrench in the works. The idea was to adjust under and use the reticle, if you follow Ted's method and go above you can do it both ways much easier to include scopes with a pre-Set zero stop.
     

    iceng

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    Every scope should have a tool less zero but a zero stop that can be set to anything.
    Every defensive handgun should be a glock, and all glocks should be 9mm.

    Fitness for purpose. I get your sentiment, but not everyone is willing to pay $2k+ for a scope.
     

    st1650

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    Every defensive handgun should be a glock, and all glocks should be 9mm.

    Fitness for purpose. I get your sentiment, but not everyone is willing to pay $2k+ for a scope.
    I have a 500$ Midas, a 1000$ Cronus and a 2200$ Leica PRS. I can set the zero stop exactly where I want on all of them. I can live with a slot to remove the cap but I think the Leica figured it out with tool less turret removal and stow a small Allen key in the windage to change the zero stop if desired.
     
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    Leatherlunger

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    Tried using the speed drop factor my last range trip, it worked excepionally well for me out to 6-700 with my 308 loads. Made some charts to compare my prime numbers at different DA’s and found for my load i get a .1 chnger ever 4k ft of DA. Pretty good flexibility for DA variation👍
     
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    Leatherlunger

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    Hey Ted, does your speed drop Excel chart have the formulas built in? If so, would you be willing to share it with us? Also, do you think it is worth making speed drop charts to find the various prime numbers associated with DA changes?
     

    Jack Master

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    Hey Ted, does your speed drop Excel chart have the formulas built in? If so, would you be willing to share it with us? Also, do you think it is worth making speed drop charts to find the various prime numbers associated with DA changes?
    Yes. the google sheet has the formulas built into them. ( sorry not in excel) Link to google sheet
    Fill in the front page drop data and the speed drop tab will automatically calculate your values.

    Yes, DA will effect your data speed number. Come read this thread where I wrote about using the system at a match. (post 23 and 24 about DA changes)
    https://www.snipershide.com/shooting/threads/holly-smokes-that-really-worked-speed-drop.7122555/
    I would not change DA for minor swings or temp or pressure, but if you're traveling it would be warranted. since there is already error in the system a little more probably won't hurt. I'd look for a minimum of 2000 DA change before I adjusted.
     

    Derrick 1981

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    Yes. the google sheet has the formulas built into them. ( sorry not in excel) Link to google sheet
    Fill in the front page drop data and the speed drop tab will automatically calculate your values.

    Yes, DA will effect your data speed number. Come read this thread where I wrote about using the system at a match. (post 23 and 24 about DA changes)
    https://www.snipershide.com/shooting/threads/holly-smokes-that-really-worked-speed-drop.7122555/
    I would not change DA for minor swings or temp or pressure, but if you're traveling it would be warranted. since there is already error in the system a little more probably won't hurt. I'd look for a minimum of 2000 DA change before I adjusted.
    Thanks for this
     

    Igor Borisov(Strelok Pro)

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    Really cool feature, if Strelok would offer it, I'd probably sell my 5700 Elite.
    Released in Strelok Pro for Android v.6.6.4
    Released in Strelok Pro for iOS v.6.81
     

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    shotie

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    Hi there to all!! New to the forum, and still trying to figure stuff out... Does the speed drop work with both FFP and SFP, or just FFP??? Also, how do l fill out my forum profile thingy?? Ol fart here from Melbourne, Australia... P.S. nice to meet everyone.... cheers....
     

    6.5SH

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    Hi there to all!! New to the forum, and still trying to figure stuff out... Does the speed drop work with both FFP and SFP, or just FFP??? Also, how do l fill out my forum profile thingy?? Ol fart here from Melbourne, Australia... P.S. nice to meet everyone.... cheers....
    If you are dialing; focal plane doesn't matter. If using the reticle BDC method you'll need to be at maximum power for a SFP.
     

    shotie

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    If you are dialing; focal plane doesn't matter. If using the reticle BDC method you'll need to be at maximum power for a SFP.
    Thanks for getting back to me.. If I run a FFP, I can still dial down the speed drop number, and use the hash marks as described... SFP as described above... Thanks guys...