Advanced Marksmanship Wind Formula Constants?

L

LR-Reaper

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Minuteman
Aug 8, 2012
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#1
The standard wind formula that I have always been taught to use is:
-Range of Target (divided by 100) X wind velocity in MPH
- Divided by the constant for the round you're using
-Equals the correction in MOA for a Full value wind.


I was wondering if anyone on here had any information on how wind formula constants were designated/created. I know the specific constants for M80 Ball, M852, and M118LR but would like to be able to more accurately use this formula for other cartridges as well. Any input on this matter is greatly appreciated.
 
#2
Re: Wind Formula Constants?

Here is how to get a constant

<div class="ubbcode-block"><div class="ubbcode-header">Code:</div><div class="ubbcode-body ubbcode-pre" ><pre>
range(100's) * wind speed (mph)
Constant = --------------------------------
Wind hold From computer

</pre></div></div>
 
#4
Re: Wind Formula Constants?

Doesn't matter, the hold is what matters, so if use the Wind Hold that in Mils you get a constant for mils if you use a Wind hold in MOA you get MOA.

It's just the math formula backwards and which ever system you use is the system that gives you the constant in reverse.

Basically you can take your actual hold or you take a hold giving to you by the computer ahead of time and insert that...

However being 2012, there is really no reason to do the long hand math and you're certainly not doing it on the fly. JBM is free online you can put your actual data in and get a wind chart from the computer for free. Print it out and carry it, no math, especially no long hand math.
 
#5
Re: Wind Formula Constants?

Thanks for all the help. I've always wondered where all those constants come from, but you're 100% right in that it is easier/more effective to just print out an accurate table and keep it with the weapon system.
 
#6
Re: Wind Formula Constants?

You still need to know the fomula(s) and should learn to do them if your head.

We're getting too dependant on computers and electronics.

Do it enough and it almost becomes automatic.
 
#7
Re: Wind Formula Constants?

Problem is, most published formulas are for one bullet and the constants provided are for a 308, and not for other calibers. So even if you memorize the formula chances are, unless you are using it specifically for the round it was originally written, it's not right to begin with. Unless of course you have done the math to adjust the constant ahead of time, which is NOT part of the published data on the formulas.

It's like rule of thumbs written in 1978, they really dont' work anymore and you have to go through the steps taken back 50 years ago to come up with new rules of thumb. Heck most of the 308 stuff out there is written for a 173gr or even a 168gr and even those, when written were more sensitive to conditions and no longer account for the advances in bullets, barrels, and powders we now use today.

The formulas are, great, but understand they were not written with the modern (or current) shooter in mind. So what you are off is probably not as helpful as you think. Unless of course you go through the trouble or rewriting the formula to fit your modern rifle.

The easier answer, go to JBM print a dope chart and wind chart for your "current' set up and then laminate it or stick it on the side of your stock for that rifle. Problem solved without the math that is really no longer applicable to what we shoot in 2012.
 
#8
Re: Wind Formula Constants?

The methods for getting constants are no different today then they were in 1978 or in 1916 when Hatcher put them in his book "Machine Guns" 1916.

You find out the constant by the formula Frank posted, paste that into your memory bank and use it.

You just have to remember if you constant is X or Y or whatever you figure out for your given round. The X or Y is what you use in your math.

Computers and BC programs are nice, but we don't want to get to the point where we can't figure out how to do the math when electronics goes south.....and they do go south.

Laser range finders are nice, but we don't want to forget how to use mils (or other methods) for ranging. GPS's are nice but we still need to learn to read a map.

Kind of like when I was working the concession stand with some 4-H kids. First thing I did was throw their calculator in the trash. They were lost because they couldn't make change. But they learned before the shift was over.

I'm not saying not to use BC programs, I'm saying learn to do the math manualy also.
 
#9
Re: Wind Formula Constants?

For field use the best method is a DA chart which there are several resources as well as programs like ColdBore that will print it out for you based on your specific rifle.

Kraig,

Aside from that one publication which, very few shooters have in their library, the constant formula stills requires the shooter to have a "hold" that worked ahead of time. So knowing the formula and having the correct data to input into the formula are two different things. You still need a starting point. JBM is a better starting point than nothing, or multiple trips to the range of trial and error. Say the shooter is not very good, and surmises that 1.2 Mils is the correct answer for the wind when in fact, poor trigger control accounted for .75 mils of correction? The formula and constant will be wrong and the shooter can be in for a long year. Software is giving you true data based on the wind and not shooter drift.

Another example, if you are a shooter with access to only a 200 yard range, then they plan on shooting someplace else beyond, say for a class or competition, without the appropriate direction in how to gather their drift, the answer may elude them. None of the current data books give you the formula and most resources that are at the shooter's finger tips only give the constants for a 308 with little or no direction that you need to adjust those numbers based off the shooter's actual cartridge and/or rifle combination. It's just not mentioned.

Out side of SH, there are very few "wind drift" resources that even give the shooter the appropriate mil constants. Most only speak in terms of MOA and a new shooter without proper direction would not know there is a difference. Granted they will eventually find and then can convert, but there are Mil Constants that take a step out of this process.

The fact this post exists shows how difficult this data can be to find. Or understand, it's not common knowledge and never has been... Even in Sniper School, you were given plug n play data, not methods of fine turning and this was pre-ballistic computers. None of the common manuals have the data either.

Because 1% of the shooting world knows, doesn't mean the other 99% entering the same world are aware. They, like most just rely on the numbers handed over to plug n play into their shooting. Then begins the journey of trial and error over a very long time, or at least until someone fills them in.

Personally I know I taught my first class here in CO, at least first real class, and I included all the formulas for reference in both Mils and MOA but I also know I link and built each shooter a data card using JBM at the end of day 1 so on day two on the range they could use that as a starting point. Then they were instructed to fine tune that data with actual results from 200 to 1000 yards, as well as confirming on several UKD targets. So I include them, but find most are not interested in doing the long hand math when resources like JBM are available for printing. Much faster and much more accurate for "their" system. The formula methods only work well after the fact not so much before. The Ballistics computers, work before the first shot it fired.
 
#10
Re: Wind Formula Constants?

To give you an ideal, I use Berger's BC Program. Lets take my Model 70 in 270 Win. and use it antelope hunting. In the morning it might be 40 degree, in the afternoon it may be 80. Every thing else being the same, there is a difference of .24 MOA in my data.

Now lets use the same data, temp being 40 degrees. Using 0 % humidity my drop from 100 to 600 is 11.36 MOA, If I put in 80% humidity my drop would be 11.35 MOA.

I don't think the antelope would notice that extra .01 moa or .06 inches on a heart lung area of about 10-12 inches.

Also I consider I never hunt past 300 yards, the above numbers are based on 600 yards.

An Altitude is a little higher. Let say I go from 500 to 5000 Ft. There would be a difference of .85 MOA or 5 inches. But if I go from my house (4500 ft) to my antelope area (5000 ft.) then the change from my zero would be 11.26 to 11.18 MOA or .08, again at 600 yards.

This is all out of my Model 70 Win Featherweight, 270 WIN, Hornady 150 gr SSTs at 2880 fps.

Take you BC program and plug in the different numbers and see what happens. I think you'll find NOT MUCH.

Just depends on what you want to do. Frankly I don't care, I don't use all that when hunting. I know what an antelope looks like at 100 yards and at 300 yards. I just sight my 270 in at 250 and shoot for hair not air. I'll never be too high or too low to 300 yards. I shot my first antelope in 1969 and my last one last one last fall, with several in between, Never had to shoot at one twice.

I realize not everyone hunts antelope, but I use them as an example. How close do you want to get, after you make that choice you can decide if you want to use averages or spend the morning doing imputs.
 
#11
Re: Wind Formula Constants?

I am amazed at how varied the wind formulas actually are. Compare the British formula that uses 10 as the constant, and the USMC that uses different constants for various yardages.
 
#12
Re: Wind Formula Constants?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: rkgsmith</div><div class="ubbcode-body">I am amazed at how varied the wind formulas actually are. Compare the British formula that uses 10 as the constant, and the USMC that uses different constants for various yardages. </div></div>

For certain applications the constant of 10 seems to be as sufficient as it is fast for a good quick hit. Kraig seems to have an effective solution for what he does, and LL seems to be a fan of another means of skinning the cat. I like the idea of having a lot of tools at hand which can help me get the job done. Thing is, the more I post and read here on this forum the more I wonder how much of this stuff is actually benefiting those who could benefit from such knowledge. That's to say, some of the simplest concepts appear to be difficult for many here to understand, or they're just not really interested in an understanding of it all as much as they are just having illiterate fun with it all, i.e. just firing a cool rifle with scope. I'm usually an enthusiastic teacher. I like showing folks how to do it, but sometimes this place as fun as it is just wears me out.
 
#13
Re: Wind Formula Constants?

RKG, I think you are confusing the British 'base wind' system with the wind correction formula. The value of 10 in the base wind system refers to the wind speed, it's not a constant to be used as a divisor. The base wind method finds a wind value that moves the bullet a given value for each 100 yards of travel. 10 MPH for example, moves the 175gr match at nominal 308 velocites about 1 MOA per 100 yards out to about 600 yards.

OP, the problem with deriving the constants absent a computer is we lack a vital number, the lag time of the bullet. Lag time is the differance between vacuum time of flight and actual time of flight, which of course is determined by air density and drag. You can get there of course, but you need downrange velocities, so two chronographs, or go through the drag tables. Pejesa's formulas will also get you there, but in the end you still just get actual drift for some ranges and back calculate a constant that gets you the desired units. I know of no PRACTICAL way to derive contstants without a ballistic program providing basic wind drift numbers.
 
#14
Re: Wind Formula Constants?

Cory, I don't mean this to be argumentive, but to get a better understanding of what you are saying.

As mentioned, I use Berger's BC Program. Taking the 270 round I mentioned above and putting it in Berger's program, using 10 MPH wind. At 100, I get .5 drift. That works out to a constant of 18.

At 300 I get a drift of 1.5, which also gives you a constant of 18

At 600 I get a drift of 3.3 of 18.

(I didn't go past 600 because this is a hunting round).

Am I using the wrong program or not inputting something I should be?
 
#15
Re: Wind Formula Constants?

I have stumbled upon a wind formula that appears to closely match the wind correction given by IStrelok and Point Blank.

Take the yardage in hundreds minus "1".
Multiply that result by wind speed(8mph - .8; 10mph - 1; 15mph - 1.5; etc.)
The result x 1 for full value, The result x .75 for half value.

Example: 600 yards, 15mph, full value
6 - 1 = 5
5 x 1.5 = 7.5
7.5 x 1 = 7.5 moa corection
7.5 / 3.438 = 2.18 mils
Istrelok - 2.00 mils
Point Blank - 2.04 mils

Example: 750 yards, 10mph, half value
7.5 - 1 = 6.5
6.5 x 1 = 6.5
6.5 x .75 = 4.875 moa correction
4.875 / 3.438 = 1.42 mils
Istrelok - 1.3 mils
Point Blank - 1.3 mils

I was surprised how close the numbers were. Point Blank did not offer partial value wind corrections. I took their result and multiplied by .75 as the formula does.

The formula treats wind as full value or half value. The formula uses .75 for half value winds.

This seems to be easy to remember and easy to use if needed. By the way it is called The Hoffman Formula.

Hope this helps someone.

Tim
 
#17
Re: Wind Formula Constants?

Kraig, you have the right idea, your numbers are fine. The constant will only start to change as the bullet decelerates enough to start increasing lag times. The 175 match for example, has a constant of 13 up to 550 yards, when 12 becomes a better fit. That works out to 700, where you should drop to 11. The 168 needs 13 as well, but that's only good to about 250, where you go to 12, then at 450 it's right down to 10.

If you ran that .270 out to say 900, you'd find the constant dropping down to maybe 16 (I don't have numbers for that load handy).
 
#19
Re: Wind Formula Constants?

Because they take the computer formula and reverse it, basically they are using the computers to simplify it as well as make it more accurate.

There are at least 4 formulas that will get you pretty darn close I can think off off the top of my head, certainly there are more.

The older one you see above, Rule of 9s, British Method, Hoffman's, the BC based one using the MPH that starts with the BC (4MPH) , it's not hard to get off the cuff, rule of thumb type formulas for wind.

But because the calls can be subjective to different people and not only what they shoot but how they shoot, you can find a host of formulas that work for a variety of people.

 
#20
Re: Wind Formula Constants?

Cory:

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">If you ran that .270 out to say 900, you'd find the constant dropping down to maybe 16</div></div>

Gotcha..

I ran the 270 numbers to 1000 and got 16.

Thanks
 
#22
Re: Wind Formula Constants?

This is what the Marine Corps was using, don't know if they changed in the last couple years.

YARDS MOA Mil
100 14 48
200 14 48
300 13.5 46.4
400 13 44.7
500 12.5 42.9
600 12 41.2
700 11.5 39.5
800 11 37.8
900 10.5 36
1000 10 34.3
 
#23
Re: Wind Formula Constants?

I know that in the Army FM23-10 there are several constants for various ranges. As I primarily shoot 175 BTHP SMKs going around 2600, I started to just use what is said in the FM 3.05.222 SF Sniper Training Manuel:

3-203. The given variable (GV) for M80 ball depends on the target’s range
(R) and is due to bullet velocity loss:
• 100 to 500 GV = 15
• 600 GV = 14
• 700 to 800 V = 13
• 900 GV = 12
• 1,000 GV = 11
3-204. The variable for M118, M118LR, and M852 is 10 at all ranges.

I've shot using both the variable number scale and just using 10 all the time, with fairly good effect on target.
 
#24
Re: Wind Formula Constants?

It's 2012, why would anyone think doing long hand math is the answer?

That stuff, while valid, is archaic, especially when you consider the time factor. It's why they create Rule of Thumb formulas, to reduce the math. Cut down the time. As well the limiting factor of the bullet, is a big downside as shooters move away from the 308.

In the field, in competition, especially in combat, your not doing long hand math. Plug and play, fire and adjust on the fly. It's more memorization of what youve seen than doing the math.

Knowing it is all well and good, but the benefit of it was not to do the math during the shot, but prior. Today we have tools to do that for you in a more effective and efficient manner. Anyone not taking advantage of that is falling behind or has already fell behind. Certainly not a single Top level Shooter today is using it. And the military suffers from inbred training and hanging onto legacy skill sets that the top Tier units have all but abandoned for modern methodology.

It's reference material , not so much working details.

 
#25
Re: Wind Formula Constants?

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">I've shot using both the variable number scale and just using 10 all the time, with fairly good effect on target</div></div>

Have you tried using a constant of 15 instead of 10?

Compairing the numbers of 175 @ 2600 using Berger's BC Program and the Army's: 100 - 1000 yards in MOA based on a 10 MPH wind.

1.21
1.19
1.16
1.13
1.10
1.14
1.19
1.16
1.22
1.29

Error using a constant of 10

0.45
0.88
1.28
1.64
1.97
2.24
2.48
2.68
2.83
2.93

Errors using a constant of 15

0.12
0.21
0.28
0.31
0.30
0.24
0.15
0.01
(0.17)
(0.40)

A one MPH error in wind estimation would be greater then the error of the difference in using Berger's program and a constant of 15 across the board.

If you do the math in your head, its easier to use one constant, after using it a bit, you can do it pretty quick. I know a lot of people here like to use computers's and such, though it would be more accurate, I don't carry one in the field. I might carry print outs to a static range, and may or may not use them. I am a fan of data books and do carry them with the same information as the print outs, but I don't carry them while hunting.

I just don't like getting too dependant on electronics.
 
#26
Re: Wind Formula Constants?

I have never, ever, not once, done such a wind equation in my head in the field. I don't even have the constants memorized or written down. What I HAVE done, is run the numbers at home, with a calculator or computer, for a few wind values. Write that down and memorise the HOLDS, not the formula. If you just use 10 mph, you can then take that hold and half it for 5, double it for 20, plus 1/2 the value for 15, etc. You just decide what the crosswind value is and there you go.

If the conversation in your head sounds like, "OK, wind 10 mph average over 600 yards, so, 600 divided by 100 is 6, times 10 is 60, divided by 15 is 4, that's in MOA so divided by 3.438 is about 1.2..." you are WAY behind the curve.

With a base wind of 5 mph, .1 mil per hundred, I think, "10 MPH, 600, 1.2...", BANG!

I can't tell you the number of times I've stood behind some students on the UKD range taking 2 minutes to get a shot out. When I ask what's the holdup, someones trying to work out some formula for wind or range. The time for that is BEFORE you get on the range, not while you are shooting.
 
#27
Re: Wind Formula Constants?

I know what my hold offs look like but I can also do the math if needed in maybe a second or two not minutes. I use a constant of 10 which appears to be good enough for M855 from an M4 out to about 600 meters. Even though this constant is wrong it is still effective. I also use this constant for EIC events at the 300 yard line shooting 77's at 2700 fps and the 600 yard line shooting the 80 grain Berger VLD at 2760 fps from my match conditioned Service Rifle. Again the constant is wrong but the math is good enough for the 10 ring when I do a good job holding elevation. The trick is not over valuing the wind. If you have a method which complements your way of learning I think that would be the way to do it. It seems there are several proponents here who have ideas about what works in their discipline. Borrow tools from another arena and you'd probably have all you need to get the job done in most any scenario. BTW, for LR competition where I have the time for math with an odd number constant I use the actual constant. I want pin wheel X's early and having the right constant better assures hasty X's.
 
#28
Re: Wind Formula Constants?

Great topic...I'm no expert when it comes to competitions, I've only shot in a couple, so my comment isn't towards competition shooters. I do know what's happening in the combat zone and not every sniper team has access to a computer and the use of wind formulas is used. Some FOB's are so remote, plug and play just doesn't happen in the units that I have experience with. There are many on SH that are active duty and learn a great deal from what's put out here. I had a discussion this week with warriors about a topic posted on SH, it's amazing what you can learn here. But to me and a lot of other old timers, the computer is a tool, to rely solely on it is setting you up for failure. Same can be said about land navigation, why learn about using a map, compass, and protractor when you have a GPS. I say good on you if you have computer to use, and even better if you can back it up by using a formula that works for you.
 
#29
Re: Wind Formula Constants?

Raider exactly what formula are you talking about, the long hand math formula or in fact on of the shortcuts ?

The idea guys are breaking out a calculator and doing long hand math, I can tell you, being USMC pre-Computer, and Pre-pretty much everything, we weren't breaking out a pad and pencil and doing the calculations, you have a set number based off the formula that is written or memorized, but as far as doing it on the fly based off the actual wind, sorry I don't know any snipers I have worked with past or present doing that.

If you are breaking out a calculator or doing math with a pencil, you are taking the long way home. I think you mis-understand what I mean by plug and play, they just plug a guess number into their shot and then play with it on the fly as they are engaging. They are not doping the shot long hand, they use a base wind call, plugging it into that distance, and then, take the shot, play with the results.

Sure there are shortcut formulas, like the British Method and Rule of 9s, but the original long hand based off the constants, I dont' know of anyone advocating the use of that formula in the field at the time of the fight ?

You're more likely to find a drop card used with wind on it, and maybe that has it based off the formula, but again we are talking about 2 different things. Using it before and using it after.

Exactly what formula are they using and how ?
 
#30
Re: Wind Formula Constants?

computers are great at the range in a controlled situation.

predator or regular game hunting....that warm glow of the screen, eyes off target for a second - not a good thing usually.

the thing i find about wind is that it's never really constant, especially when shooting longer distance.

so there is value in having familiarity with reading wind and its effects on the environment (swaying of trees, leaves, grass, etc.) no matter what year it is.

the only true constant is that it's a guestimate no matter whether using a computer, long hand math, wind flags, etc. by the time you think you have it figured out, it changes speed and usually direction making the previous calculations less than applicable.

IMO the best formula...experience shooting in wind (on purpose) and a good memory or data card based on those conditions experienced before.
 
#31
Re: Wind Formula Constants?

I really don't see the big deal with doing math in your head.

Lets take the CMP GSM Vintage Sniper Match. I cover it in my clinics as a GSM MI.

Look at the 600 yard stage. You have 15 shots, the target comes up for 20 seconds and you fire, then down for 20 seconds.

Most people use the '06 round. At 600 the "10" constant works great.

So you take a gander at the target area and blowing tree give you the estimate of 12 MPH. How long doe it take to say in your mind 6*12/10=7.2 or hold/click 7 min into the wind?

Do it again. after the first shot, the target goes down and you have another 20 seconds to look in the spotting scope and get another reading of the wind, make the estiment, correct and as soon as you see the target start to wiggle, adjust or favor, let the bolt go forward and fire when the target reaches the top. Use the rest of your 20 second firing time to mark the last shot and plot your call.

If you learned your multipalation tables in grade school its no problem. It's not a complicated math problem that requires calculators or pencil and paper.

Just an example. It works in hunting or other areas where time is limited. it it takes you more then a couple seconds you have other problems.

A constant of 10 isn't perfect, but it will keep you in the X-10 ring.
 
#32
Re: Wind Formula Constants?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: kraigWY</div><div class="ubbcode-body">I really don't see the big deal with doing math in your head.

Lets take the CMP GSM Vintage Sniper Match. I cover it in my clinics as a GSM MI.

Look at the 600 yard stage. You have 15 shots, the target comes up for 20 seconds and you fire, then down for 20 seconds.

Most people use the '06 round. At 600 the "10" constant works great.

So you take a gander at the target area and blowing tree give you the estimate of 12 MPH. How long doe it take to say in your mind 6*12/10=7.2 or hold/click 7 min into the wind?

Do it again. after the first shot, the target goes down and you have another 20 seconds to look in the spotting scope and get another reading of the wind, make the estiment, correct and as soon as you see the target start to wiggle, adjust or favor, let the bolt go forward and fire when the target reaches the top. Use the rest of your 20 second firing time to mark the last shot and plot your call.

If you learned your multipalation tables in grade school its no problem. It's not a complicated math problem that requires calculators or pencil and paper.

Just an example. It works in hunting or other areas where time is limited. it it takes you more then a couple seconds you have other problems.

A constant of 10 isn't perfect, but it will keep you in the X-10 ring.</div></div>

That's the way I do it. It's the way I was taught to do it, and it's the way latest USAMU SDM program shows how to do it. Seems to be as effective as it is fast. Students usually can get a handle on it with just a few minutes on the topic.
 
#33
Re: Wind Formula Constants?

My bad, I should have said range constant. The wind formula is the same as when you and I went to school and is still being taught at the school house today. R x V (full/half/quarter) / Constant. The only thing that has changed over the years is what range constant to plug in. This formula has proven that you can work it in your FFP as you see the winds, just as you would a PDA if you have one. I guess we were the exception to the rule because we did use it in the fight. I have engaged and corrected at distances where my spotter and I could not see impact. I have engaged and corrected off which way the bad guys jumped...no kidding! But since our FFP's were tentative until I put my boot on it, we were never rushed...well in Fallujah in 04 we were a little. Just wondering, when you teach a course do you advocate taking your data book with you on a combat patrol and if so, why?
 
#34
Re: Wind Formula Constants?

P.S. don't get pissed at me and not send my target order out...looking forward to see what maxium pain we can get out of it.
Looks like a well thought out target, and we'll put it to the test this Thursday.
 
#35
Re: Wind Formula Constants?

My dope is mostly memorized and really all you need with the rifle is one of these :

Impact Databook Stick On

There isn't much more data needed to be carried and relies on no math, no batteries no calculator

or you can use an FDAC, which takes up no space, no weight and is effective under changing conditions

FDACBOLTCOMP.3.jpg


Full blown version that does wind, leads, etc,
FDAC Complete image
AdaptiveQuickCard2-600x358.jpg


Unless you are required to sit in one place, draw a sketch, make a range card, carrying a small laminated cheat sheet is the easiest way to skin the cat. The wrist commanders are enough.

windchart.jpg


photo.jpg


Again, no math, no batteries, made for the system being used.

last match I actually just carried a single laminated page from JBM and used that entire match. carried the PDA but never bothered to use it. Only in the downtime will I use it.

Now in an ELR situation where distance gives me time and opportunity and the target priority is much more important, then the PDA is impossible to beat. UKDs beyond 1000m, the laser and PDA combo is the ticket. But inside 1000 yards, I can recite my dope in both mils and moa without the aid of reference, and usually I know what my wind will be before I pick a target. There is no need to do the math, I know what I am holding by the range, I shoot enough I have no need for math, or even charts 90% of the time.

Prior proper planning and all.... but for accuracy, the computer makes it much easier, even without an internet connection, you can use Excel to print the sheet above that Lindy uses.
 
#36
Re: Wind Formula Constants?

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">when you teach a course do you advocate taking your data book with you on a combat patrol and if so, why?</div></div>

Understand, this was a while ago, I taught my last military sniper school in the early 90s ('91 I believe). Things changed I'm sure.

I am and always have been a sticklier for good data/score books, BUT, I taught not to take a data book to the field. If needed, when the OpPlan you did a range card if needed but with limited information. You go in steril. Too much info on a data book that no one else needs to know in case something happens.

You can make notes in the field to be added to your data book later if necessary.

The range card should have the information you need for the mission without conformising anything else.

Like I said, things are differnent now, base on the books I've read on present sniping they don't send out one or two man teams to work alone for extended purposes like they use to.


 
#37
Re: Wind Formula Constants?

I just bought a FDAC, haven't had the time to work with it yet. Waiting on my new scope with mil/mil adjustments to come in...who said old knuckle dragging grunts can't learn something new. Is the something that is replacing the mildot master? or reinforce it? Where did you get the arm band, will a map marker pen stain the plastic? Looks like a good set-up and something worth looking into.
 
#40
Re: Wind Formula Constants?

Now that i'm in the LEO business I agree, it's a piece of gear that is hardly broken out of the ruck. We do have sketch kits where information is stored. We don't do range cards in LE work, it more of a site diagram because we don't engage out to the maximum effective range of the weapon and we're close enough that it can be sent back to the command post to serve as a visual representation of what we're seeing and if deadly force is used it becomes part of the incident report and AAR.
 
#41
Re: Wind Formula Constants?

OP,

I've used the free ballistic calculators to get wind holds and tried them in the field. I plot my shots and review the results. Thus far the calculators have worked for me once I got the data to come out of them that matched what I saw in the field. I must say that I picked up the need to find a rule of thumb from the Magpul DVDs and modified it to fit the information I had given to me by JDM and Shooter as well as the results I've seen in the field.

Like Frank and others have advised the best information is what you learned from using the calculators as well as what you learned from shooting. The rule of thumb that I keep in my head goes like this:

This is a .260 with a 130 gr. VLD @ 2950 fps

When the DA is from 0' up to 2000'

.1 Mil per 5 mph wind (3 or 9 o'clock) per hundred yards, minus .1

So for 5 mph at 600 is .5 Mil, 10 mph would be 1.0 Mil

This is true to 800 yards then I stop subtracting the .1 Mil. So 800 is .8 Mil hold per 5 mph, 900 is .9 Mil per 5 mph

When the DA exceeds 4000' (rare for me, where I shoot) I subtract the .1 Mil all the way out.

It's been a hard learning curve going from a .308 with 175 SMKs or 178 A-maxes to the .260 I've had a bunch of misses in competition due to holding .308 windage and not .260 windage. I'm not saying this is the best rule of thumb out there or even the best one for my rifle ,but as of the last six months it's been working.
 
#42
Re: Wind Formula Constants?

I marvel at the results many obtain from calculation. I think I see a conviction in them that one can make predictions about POI's that are down to the decimal. Alas, this has almost never been the case for me.

There's that last bit of uncertainty, remarkably very small, that inevitibly plagues us all.

Last night, I watched the Science Channel premier of <span style="font-style: italic">The Code</span>. This series explains the significance of numbers in the science that lies behind essentially everything in the Universe, and in the episode <span style="font-style: italic">Prediction</span>, the concept of Chaos Theory is rather elegantly (as are all the other concepts they cover) explained.

I often make effort to explain/simplify basic physics mechanisms; but I seldom attain the clarity and simplicity this series achieves.
If you really want to understand the priorities to assign various factors in your shooting efforts and achievements, I believe this series can be of immense help.

Greg
 
#44
CoryT said:
I have never, ever, not once, done such a wind equation in my head in the field. I don't even have the constants memorized or written down. What I HAVE done, is run the numbers at home, with a calculator or computer, for a few wind values. Write that down and memorise the HOLDS, not the formula. If you just use 10 mph, you can then take that hold and half it for 5, double it for 20, plus 1/2 the value for 15, etc. You just decide what the crosswind value is and there you go.

If the conversation in your head sounds like, "OK, wind 10 mph average over 600 yards, so, 600 divided by 100 is 6, times 10 is 60, divided by 15 is 4, that's in MOA so divided by 3.438 is about 1.2..." you are WAY behind the curve.

With a base wind of 5 mph, .1 mil per hundred, I think, "10 MPH, 600, 1.2...", BANG!

I can't tell you the number of times I've stood behind some students on the UKD range taking 2 minutes to get a shot out. When I ask what's the holdup, someones trying to work out some formula for wind or range. The time for that is BEFORE you get on the range, not while you are shooting.
Click to expand...

I know this thread started a couple of months back But I find that some of the numbers dont work out and I have tweaked them to see if they match my ballistic tables for the 7.62/.308 175gr BC.496 at 2800fps with a temp of 59*f

So with 600yds with a 10mph wind, 6x 10=60 devided by 14=4.285 moa yet my software says its -4.8 which @ 600yds is going to put me out by 0.514 moa out which at 600 will be 2.947" out, and at 1000yds 10x10 devided by11 = 9.090909 and my software says it should be 9.5moa so at 1000 im gonna be 4.283" off,

But with the 700 and 800yds being devided by 13 works OK on 700yds but on 800yds 8x10 devided by 13= 6.153 when the software says its 7.0 which puts me out by 7.087" . it works better if I devide it by 12.5 because i then get and moa of 6.4,

can someone tell me why or what is wrong here as now I dont know which to believe in, SEE this is what happens when you go hi tech, I'm not sure if this is a good thing anymore,

Thanks Guys, john
 
#45
2800fps from a 175gr ? That is a lot, are you sure about that number, if you are indeed going that fast, I would suggest changing the BC and trying .505...

These formulas are just a "STARTING POINT" you have to shoot it to determine how your load / rifle / shooter combination works which is why we use datebooks. Neither the software, or the formula can figure you or your system in, it is just giving a general starting point to work with. Every rifle and shooter are different. You my have a 1/4MOA bend to your shooting style that moves the bullet one way or the other. You're barrel, load, etc, all matters which is not figured by any of this.

These are not written in stone.

At the end the day, BELIEVE THE BULLET and write it down. Then after you have enough data, you can tweak the program to match your actual dope.
 
#46
Now that i'm in the LEO business I agree, it's a piece of gear that is hardly broken out of the ruck. We do have sketch kits where information is stored. We don't do range cards in LE work, it more of a site diagram because we don't engage out to the maximum effective range of the weapon and we're close enough that it can be sent back to the command post to serve as a visual representation of what we're seeing and if deadly force is used it becomes part of the incident report and AAR.
Click to expand...

Something else you might consider. You can go to the city or county engineer and get a "to scale" lay out of your city. With that you can have your range finder. You study the plates and you can get the angles for shooting from different building, learn the prevailing winds and flat get to know your city.
 
#47
Lowlight said:
2800fps from a 175gr ? That is a lot, are you sure about that number, if you are indeed going that fast, I would suggest changing the BC and trying .505...

These formulas are just a "STARTING POINT" you have to shoot it to determine how your load / rifle / shooter combination works which is why we use datebooks. Neither the software, or the formula can figure you or your system in, it is just giving a general starting point to work with. Every rifle and shooter are different. You my have a 1/4MOA bend to your shooting style that moves the bullet one way or the other. You're barrel, load, etc, all matters which is not figured by any of this.

These are not written in stone.

At the end the day, BELIEVE THE BULLET and write it down. Then after you have enough data, you can tweak the program to match your actual dope.
Click to expand...

Thankyou for your quick reply, Regarding the speed, from the Ballistic program for my range finder (Put together by Sierra) I looked up sierra branded .308 175gr HPBT match King @2900fps which i have to set the range finder at (F) but when I down Loaded the Ballistic Data they then listed the FPS @ 2800 with a BC of .496 which is a little confusing so I loaded this data in to my software and it all developed a mind of its own, Although I think it would be better at around 2600/2650fps,

So do you think by raising the BC data to .505 it would balance the figures better, I must admit I was worried about that velocity becoming a Barrel Burner at 2800 and I would like to find a more stable flight patten because although the high FPS gave less drop I cant get this nagging feeling out of my head that it might make it wonder alot,

Thanks again, John
 
#48
MilDot1960 said:
Thankyou for your quick reply, Regarding the speed, from the Ballistic program for my range finder (Put together by Sierra) I looked up sierra branded .308 175gr HPBT match King @2900fps which i have to set the range finder at (F) but when I down Loaded the Ballistic Data they then listed the FPS @ 2800 with a BC of .496 which is a little confusing so I loaded this data in to my software and it all developed a mind of its own, Although I think it would be better at around 2600/2650fps,

So do you think by raising the BC data to .505 it would balance the figures better, I must admit I was worried about that velocity becoming a Barrel Burner at 2800 and I would like to find a more stable flight patten because although the high FPS gave less drop I cant get this nagging feeling out of my head that it might make it wonder alot,

Thanks again, John
Click to expand...

No,

Clearly you are guessing what your BC and MV is, what Sierra got and what your rifle shoots is two different things...

That is the advertised BC based on that velocity, that is NOT what your rifle shoots.

This matters... Garbage in, yields garbage out... you cannot swag data points and expect to be right
 
#49
Well thanks for clearing that up, this is what happens when someone who does it old school goes out and buys ballistic gizmos, thats a lesson well learnt,

thanks again, John
 
#50
Remember, all this published data is designed to give you a starting point, in reality they are hoping to help you hit a 6 ft X 6 ft Target some where, that is it.

They are saying,

"If your rifle shoots the 175gr SMK at 2800fps, you can expect to use the average BC of .496, if your bullet is going 3000fps you can use .505, etc."

They figure you are gonna shoot it on paper, like at a Highpower Range and then you'll record your actual data... it's why you can get Sighters in High Power. They just want to start you off on paper with an average number that should get you on that 6ft Square board.

You need to chronograph and / or shoot on paper then record your data. Absent of a Chronograph, if you shoot and record your data, you should be able to reverse engineer your numbers with the Ballistic Computer to get you close. Then when you shoot again under slightly different conditions the computer will get you closer than the manufacturers average.

There is no magic bullet, it takes effort and equipment to line the software up. Once that effort is done, the software will then work as advertised for YOUR SYSTEM.
 
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