The 5 environmental factors that affect accuracy (With Video)

July 30, 2010 by  
Filed under Trail Boss Videos

The five (5) “environmental” factors that affect accuracy — Temperature, Humidity, Elevation / Barometric Pressure, Wind, and Light. Keep in mind when we are shooting to put food on the table or other reasons we are not shooting a match where we are trying to put all of the bullets through the same hole. Temperature affects our shooting in several different ways:
It affects the trajectory of the bullet. It affects the temperature of the barrel, It affects the ammunition we use, It affects the performance of the shooter.

A second effect that results from warm or cool outside air temperature relates to how hot your barrel becomes during your relay. On a relatively cool day (50 degrees), the outside air is able to absorb more heat from the barrel at a faster rate than it does when the air temperature is 80 or 90 degrees. This helps to keep the barrel cooler with fewer harmful side effects like “baking” the fouling in the barrel which in turn can result in a significant loss of accuracy. Even on a moderate day (60 degrees) the barrel can become too hot to hold. Heat — especially excess heat — can play havoc with your ammunition. Even if you have taken the proper steps to keep your ammunition cool prior to coming to firing , setting you ammo in the direct sunlight or clambering it in a hot rifle for any length of time can result in an errant flier. I always keep my ammunition out of the direct sun that is why I do not use loop loaders.

Keeping yourself  cool and comfortable is an important element in the overall accuracy equation as well. If you becomes overheated or dehydrated, not only does he or she become uncomfortable, but their physical senses are affected — vision deteriorates as moisture is drawn from the eyes and brain by outside heat, sweat running down the forehead can cause problems seeing the target, high blood pressure results from low water content in the body along with fatigue, weakness, lower back pains, inflammation, headaches, etc… — the list is a long one. Staying fully hydrated is very important for anyone in the heat . Drink lots of  water (no carbonated beverages or even a  little alcohol). Drink often don’t wait until you’re thirsty. By that time you are already dehydrated.

Many shooters believe that humidity (i.e. the amount of moisture in the air) can have a serious impact on accuracy. The theory is that air containing a high degree of moisture must be more dense than dry air. As a result, it must offer more resistance to a bullet in flight than does dry air. The fact of the matter is that the amount of humidity in the air has virtually no effect on bullet accuracy. That’s because a water molecule weighs less than a dry air molecule. Yes — that’s what I said. Moist air is actually less dense than dry air. In fact, when the surrounding air is said to have 100% humidity (i.e. it is holding as much water vapor as it can at its current temperature), it still only contains 4% moisture. Look at the numbers for yourself:

Elevation and barometric pressure can definitely have a significant effect on the accuracy of your load. Why? Because they affect the density of the air, and therefore, the amount of resistance it exerts on the bullet as it travels to the target. Elevation is generally expressed in “feet above sea level”. The performance of a load at sea level is much different than it is when fired at an elevation or altitude of 5,000 feet above sea level.  A bullet fired at a 5,000 foot altitude has a trajectory which is 62.31” inches flatter, 28 feet per second faster, with 54 additional pounds of energy upon impact. That’s why it’s so important for hunters to check their rifles once they arrive in camp when they travel to higher elevations to hunt such big game animals as elk, caribou, bear, and moose.

Many shooters immediately grimace at the thought of having to deal with wind. But it is not that big a deal at 100 yards or less, in fact it is no deal at all. At extreme long range like 1000 yards, it can be a big factor, however  just wait for the gust to stop and take your shot.  Wind is also a good thing when it is steady and predictable. As long as it acts as a constant and not as a variable, we can calculate its effect on the flight of our bullet and make the necessary adjustments to compensate for it accordingly. It’s when the wind is unpredictable, gusting, and erratic that it plays havoc with us. Over the course of 1,000 yards, the wind can actually be blowing in several different directions at the same time. But lets face it most of us do not make shots at this distance except fr fun.

The fifth and final environmental factor that we need to consider when shooting  is Light — or said another way, the quality and amount of light that is illuminating our target. Although a certain amount of light is falling on our target throughout the course of a day’s match, the intensity of the light and its effect on our ability to “see” the target clearly is constantly changing.

Copyright © 2010 by Steven L. Doran All rights reserved under international and Pan-American copyright conventions. No part of this article may be reproduced or utilized in any form or by any means without written permission from the author Steven L. Doran.

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2 Comments on "The 5 environmental factors that affect accuracy (With Video)"

  1. Steve in Merritt Island on Mon, 9th Aug 2010 6:20 AM 


    How do you adjust for the barometric pressures? Here in Florida, especially with the commonplace short summer afternoon storms, the static pressure drops, then flies up in short order. As I live near the Atlantic coast at sea level, the sea breezes push the rains in fast.

    Would this sudden drop and sudden rise continually knock out my zero? While I own three scoped rifles, the only one I shoot regularly is my Win 9422, and then only at short distances (generally less than 50 yds.). I do note that when I do shoot the centerfires (perhaps 3x year), I am fiddling with elevations, not so much windage. Perhaps upwards of two inches at 100 yds.

    Intersting article and I am now interested enough that I will head to the range later and take some actual written notes (noting ambiant temps and static pressure) for a change.

    Steve in Merritt Island

  2. John Broekhuizen on Mon, 9th Aug 2010 7:32 AM 

    It will not be enough for you to notice at 200 yards and under unless you are trying to put the same bullet through the same hole it will not be a big deal

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