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Intro to guesstimating windage for long range shooting

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posted on Apr, 22 2011 @ 09:53 AM
Most of what is written is a general guideline... Some I took straight out of the Marine Corps Sniper training Manual... call it a tip on long range shooting and none of these rules are set in stone... every shooter has his or her own methodology... this one is a combo of years of hunting and Marine shooting experience... so if your new to the wonderful world of long range shooting... here is a starting point...

Wind poses the biggest problem for the shooter. The effect that wind has on the bullet increases with range. This is due mainly to the slowing of the bullet's velocity combined with a longer flight time. This allows the wind to have a greater effect on the round as distance increases. The result is a loss of stability.

Since the shooter must know how much effect the wind will have on the bullet, he must be able to classify the wind. The best method is to use the clock system. With the Shooter at the center of the clock and the target at 12 o'clock, the wind is assigned the values: full, half, and no value. Full value means that the force of the wind will have a full effect on the flight of the bullet. These winds come from 3 and 9 o'clock. Half value means that a wind at the same speed, but from 1,2,4,5,7,8,10, and 11 o'clock will move the bullet only half as much as a full-value wind. No value means that a wind from 6 or 12 o'clock will have little or no effect on the flight of the bullet…

• 1-3 mph will move dry tall grass
• 2-4 mph - you can just feel on your face, large leaf, light stems move like maple leaves
• 4-8 mph – will make small leaf, heavy stalks move like alder
• 5-6 mph - mirage tips 45 degrees – flat lines a 24” piece of flagging ribbon
• 6-10 mph – will move the tips of short needle trees like larch & spruce
• 8-12 mph – will make brush like alder, small aspen etc start to move
• 10 mph – mirage starts to flat line
• 10+ mph will make trees start to move
Under favorable conditions, an expert shooter will estimate the wind speed in 2½ mph increments. Sharpshooter wind reading would be in 5 mph increments.
At 300 yards, the range your rifle is zeroed for and that you will be practicing at, a sharpshooter adjusts his windage in whole MOA increments and an expert adjusts his in half MOA increments. By "favorable conditions" I mean one of two things:

(A) There is smoke or dust nearby, allowing you to measure the wind by how fast it is drifting, or

(B) It is a hot day and there is an object with a well defined horizontal edge near the target on which you can see the mirage. "Mirage" refers to the heat waves which rise off of hot objects. It is easier to observe in a 50x spotting scope than in a 10x rifle scope, but it is still visible. You can see it with your naked eye if you look across the hood of your car on a hot day. In still conditions, heat waves appear as wavy vertical lines. Five mph winds bend them over at about a 30º angle while ten mph winds bend them over at about a 60º angle. Fifteen mph winds bend them over flat so it is no longer feasible to measure the wind speed this way. If you look at a horizontal edge, like a rooftop, the heat waves seem to be running along it.

Open air moves faster than air close to the ground, if you are on a canyon wall and the wind is 10 mph it is a pretty safe bet that in the open of the canyon where you have to shoot across it will be 25-50% stronger.

Wind speed estimation takes practice. With practice you can get very good at making an accurate estimate of wind speed and affect, however no matter what it will always be you best guess it is not an exact science for the field shooter.

If you are going to be estimating the wind speed in either 5 or 2½ mph increments and it is important to be systematic about adjusting your windage dial in only those increments. Just because your scope has quarter MOA clicks does not mean you are going to be using them all. At 300 yards a 10 mph wind requires 2 MOA windage, so a 5 mph wind requires 1 MOA and a fifteen mph wind requires 3 MOA. So, for sharpshooter level wind reading, you will be adjusting your windage dial only in whole MOA increments. Do not make any finer adjustments until you are confident that you know the difference between a zero, five, ten or fifteen mph wind.

Below is a 300 yard rosette of the type popularized by James Owens, but with MOA adjustments consistent with the Aguilar System for Medium-Range Sniping. Double all the MOA adjustments for 500 yards. I do not really recommend the use of rosettes, but I have included one for the benefit of student just learning the art of long range shooting.

One Handy formula for windadge comes from my Beloved Marine Corps…
o Conversion of wind velocity to minutes of angle
(The Table below is based on the USMC .308 M24 sniper rifle your ballistics will vary depending on your weapons caliber)
All telescopic sights have windage adjustments that are graduated in minutes of angle or fractions thereof. A minute of angle is 1/60th of a degree. This equals 1 inch at 100 meters (1.145 inches). Snipers use min. of angle (MOA) to determine and adjust the elevation and windage needed on the weapon's scope. After finding wind direction and velocity in MPH, the Sniper must then convert it into MOA using the following formula. This formula is a rule of thumb only and is used as a starting point. Practice and keeping a good data book are the ultimate goals and tools.
RANGE (1st digit) x VELOCITY (MPH) = MOA (for a full value wind)
CONSTANT ( for a half value wind divide this answer by 2)
The constant depends on the targets range:
100-500 meters "c"=15
600 meters "c" =14
700-800 meters "c"= 13
900 meters "c"= 12

well there you have it... now what are you waiting for... go shoot something

edit on 22-4-2011 by DaddyBare because: (no reason given)

edit on 22-4-2011 by DaddyBare because: (no reason given)

posted on Apr, 22 2011 @ 10:04 AM
reply to post by DaddyBare

wonderful and valued..


posted on Apr, 22 2011 @ 10:06 AM
Wow great post thanks for posting this.I like to shoot and have been doing so since I was a boy.I recently became interested in long range shooting and am searching for a place near me where I can practice. Your post will help a great deal. I would personally like to thank you for your service. You guys deserve all the thanks I can offer. I try to thank every service member any time I meet one. That goes for vets too.

posted on Apr, 22 2011 @ 10:07 AM
reply to post by DaddyBare

Well done.

posted on Apr, 22 2011 @ 10:11 AM
Good information. Thanks

That beats cracking a can and walking em in any day.

posted on Apr, 22 2011 @ 12:21 PM
Real good read for the people that understand ballistics and have spent numerous/countless hours behind a firearm.

The Corps have long produced some of the finest shooters on planet earth and anyone who does a fair amount of shooting should really take note of some of the external factors that natures gives you for wind.

I dont know how many people are going to making shots at over 300 yds where I am at, but for those of you who will be bugging out to places that have this scenario, this is real good info to have and I would even take it a step further and mark out in 100yd incriments with some type of natural looking marker.

I would plant a tree or bush, something that is not obvious to someone who is creeping up on your location. I have found in my year of shooting at long range that having the yardage was better than having the windage, but I have never made a shot over 400 yds either.

The 223/5.56 nato is a pretty accurate round and will do plenty of damage at 300 yds, but it does get pushed around at yardage over 200yds with anything over about a 10mph wind.

EDIT-I didnt read all the way through because I have seen the information before, but I did forget that info was based on the .308/30cal balisitics.

bottom line, if you are buying firearms as part of your BOB or for defensive measure. Put a few rounds down range every month so you what you have in your hands
edit on 22-4-2011 by armtx because: (no reason given)

posted on Apr, 22 2011 @ 01:00 PM
For 5.56mm (on an L85 A1) I was taught:

100 Metres. No real change in POA (unless it's very strong wind then a shade into the wind to compensate)

200 Metres. For a Fresh Wind - Aim half a man-sized target width in direction of wind
For a Strong Wind - aim one man-sized target width in direction of wind.

300 Metres. For a Fresh Wind - Aim one man-sized target width in direction of wind.
For a Strong Wind - aim two man-sized target's width in direction of wind.

This is assuming the wind is blowing at right-angles to the target.
If it's at a diagonal angle then halve everything...

The OPs guide is good, no doubt. However it's not so good for a quick aquisition guide which is what we were taught.
edit on 22-4-2011 by WatchRider because: amendment

posted on Apr, 22 2011 @ 02:02 PM
reply to post by WatchRider

Thank you and your right...
Mine is not a quick acquisition guide.. obviously since I'm talking about 1/4 MOA and not kentucky windage...
not everyone out there is gonna want to be a precision shooter at 1000 yards their happy to hit anything at 100 yards...

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