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|01-24-2010, 08:42 PM||#1 (permalink)|
Doping: Refining shot placement
It's Called Dope
from Issue # 30, Winter, 1999
Prior to beginning this article, it is necessary to say that there is an awful lot of information about dope. Who you talk to will make a difference in what you hear, like any other subjective issue. My intent with this article is to provide the reader with what will work. People engaging in rifle shooting activities have longingly looked for ways to simplify doping, some easy formula that will work 100% of the time in any condition with an exactness that will place their shot in the middle of the target every time, on any given range. If this were available we could simply print the formula, end of article. The fact is, its not that cut and dried. Doping is an art. Something that is developed and acquired with the experience of shooting long range over a period of time.
This article will provide information for both the novice and the professional marksman.
Before continuing I want to define what I mean when I speak of dope and doping.
Dope: The observed information about conditions that will cause affects on bullets in flight at a particular location at the present time.
Doping: The art of transposing observed information to the equipment you have at hand for the purpose of refining shot placement.
While this is a study of exterior ballistics, I am going to move forward from this point with the belief that you already know the zeros for your rifle at a variety of distances. We know if we return to the same range and experience the same conditions, with the same gun and same ammunition we can most likely reproduce the same shot placement as during our previous outing.
Our study will look only at the variation of conditions possible between the rifle and the target, and the factors causing change in bullet impact. Those factors are:
b. Available Light
e. Wind, its direction and velocity
Let's examine each of these causation separately, saving wind for last.
A rise in temperature can increase velocity. Increased velocity will cause the impact of your round to be higher than your zero.
Examine this scenario.
Our rifle was zeroed at three hundred yards with a specific load when the temperature was 60F. We have to deploy at 80F. The only thing that has changed is the temperature. The general rule of thumb is that this shot will print one minute of angle higher than our zero. This equals three inches on our target.
One minute of angle is equal to one inch per every one hundred yards.
An increase of fifteen degrees will displace a round one minute high at 600 yards. And a 10 degree change will cause one minute displacement at one thousand yards.
As a tactical shooter we may overlook this, as it might not seem necessary for the average shot distance involving police. Think about where our gear and ammo are generally stored? Most officers still deploy from the trunks of their car. How hot or cold does it get there? My experience indicates you can expect as much as 40F change on some days.
Utilizing a thermometer when training, and recording temperatures in your log is important to your conditions evaluation. If you can keep your ammunition out of direct sunlight, you can avoid some of this problem. I store a thermometer with my ammunition.
Did you ever wonder why you put on clicks in the morning and then take them off in the afternoon? A change in temperature may have been the variable not taken into consideration.
The direction of light and its intensity can change where the target appears to be. Iron sight shooters have held fast to a general rule for many years, "sun up sights up, sun down sights down".
When the sun is bright a distortion will form around the target. This generally causes the shots to print low, the target appears to be higher than it is. When cloud cover exists, there is very little or no distortion. The tendency is to hold closer to where the target really is, which will result in a higher than expected shot. The brighter the sun the bigger the target will seem.
How much displacement depends on the brightness of the sun and the distance you are from the target. Training in variable conditions can increase your hit probability.
ELEVATION and HUMIDITY
We have to evaluate the effect of air density, which produces drag placed upon the bullet in flight. The higher the altitude the thinner the air. Given a zero at a lesser altitude your bullet will print higher when fired in the higher elevation. Humidity is simply the amount of moisture in the air. Moisture in the air places drag on the bullet. The more moisture the more drag which will cause your bullet to print lower.
How much displacement depends on how much conditions have changed from those when zeroing, and as usual, how far we are from the target.
If you work in an area where the probability exists that you may be deployed at different elevations, you should have zeros calculated for each variation.
Barometric pressure normally ranges in the area of 29.0 to 32.0 psi. Decreases in barometric pressure will decrease the density of the air and allow the bullet to impact higher on the target.
The following chart illustrates the approximate change of impact from sea level to ten thousand feet, given the rifle was zeroed to point aim, point impact at sea level. The chart is also dependent upon shooting match grade ammunition in .308 Winchester caliber at approximately 2600 feet per second.
IMPACT RISE WITH CHANGE OF ELEVATION IN MINUTES OF ANGLE.
The information in this chart is computer generated and is generally reliable. However, it does not take the place of actual dope developed by the marksman. Use this information for reference only.
WIND, its DIRECTION and VELOCITY
On the average police shootings, involving rifles, involve distances of less than 80 yards. Within this distance wind affect upon shot placement is very little. Let's refer to this statistic as our average shot. If these were the only shots we ever had to make, there would be very little reason for a discussion on wind.
So we are going to move the target down range and talk about other than average shots. We need to discuss this for two reasons.
a. The potential is there to require such a shot.
b. We still have to hit where we are aiming.
At this time it should be obvious that the distance from the target will dictate the amount of adjustment required to compensate for given conditions. This is true because the farther you are, the longer the bullet is in flight. The longer the bullet is in flight the more time conditions have to influence its travel.
On ranges of known distance the flag method is the system most often used to determine wind direction and velocity. Flags or wind socks are placed on poles to be up range of the target. The shooter views the flags to determine direction. By calculating the angle of the flag and dividing by a number representing the caliber of the round being fired the shooter can determine velocity. An explanation of this method can be found in most rifle data books. A lot of people use this method, but for the life of me I can't figure out why. I suppose, like a wind reading instrument, taking the flags into account with everything else provides the shooter with more information that can verify their decision. Here are the problems with flags.
a. Flags fly high above the berms; the bullet don't. So generally the wind at the flag is not the condition that will affect on the bullet in flight.
b. Looking at flags across a long range will generally provide you with conflicting information, as wind conditions are seldom consistent over a long distance.
c. Depending on the weight of the flag, the material its made of, or the amount of moisture it has collected, the wind will move it differently.
d. Flags do not respond quickly to change.
I'm sure that more rationale in this matter is available, but these are the primary reasons why flags are not my choice.
From the tactical shooters perspective whatever you can see moving, between you and your target, is of importance. Make sure its between you and your target. Don't fall victim to false indicators. A directional vane on the roof is no indication of what occurring at ground level between buildings. Look for things like a flag attached to the side of a house, clothes on a line, hanging plants or flowers, (not the whole hanger, the plants inside) wind chimes, hanging bird houses and feeders, lawn ornaments that twirl in the breeze, even swing sets, water rippling on the surface of a pool, or pond.
Wind moves very differently around buildings. Your favorite radio station may tell you that the wind is out of the West today. This is not an indication that this is the condition where you are. Sometimes wetting your finger and holding it up in the breeze is as good as you are going to get. Incidentally, the cold side will be the way the wind is coming from.
For that long shot that we have to hurry up, get into position and then are put on hold. Most people in the business have experienced this more than once. While on hold, conditions in the wind have to be monitored. A dominant condition must be determined. Dominant condition is simply that condition that prevails most of the time.
Then we look for variations in the conditions. The best way to do this and any other wind analysis is by looking at mirage through a spotting scope.
Mirage is simply heat waves reflecting from an object. The warmer the day the more mirage you will see. Anyone who has watched a fire has noticed the distortion that develops from the heat. This distortion is what we look for in the scope. When these waves are observed, movement will be identified. The direction of that movement is the way the wind is blowing at that specific place, at that specific time.
Mirage is best captured by focusing on the object you are reading and then turning the scope slightly out of focus. Your ability to see the distortion will improve. You're looking for movement in the heat waves themselves. Watch the waves bend, to see the affects of the wind and read the wind direction.
The best place to read mirage is where you can. Ideally you want to be halfway between you and your target directly in the path the bullet will travel. However, ideal is not what is always available. You may have to improvise, at a different distance, look for a sand box, automobile, pavement, window sills, basically anything that is in the sunlight.
Watch the waves and observe the changes. Remember that wind is rarely constant. This brings up a critical point. When you dope the wind, you have to shoot the wind. Don't dope for a ten mile an hour wind and then wait for a lull in the breeze to shoot. Guess what? You are going to miss. You must be observant to change and change with the conditions. A marksman who stays in position for an extended period will change sight settings several times. It is not uncommon for competitive shooters, at six hundred yards, to make adjustments four or five times in a twenty minute string of fire.
If the mirage is moving vertically, it is called boiling. This is an indication the wind is moving very slowly or is non-existent. Many people think that this is the time to deliver a shot, it isn't. This vertical distortion makes the target elongate, appearing higher than it is. This perception increases at greater distances. Most competitive shooters will not launch a round in this condition and to them there is only an X-ring at stake. I would say if competition shooters shy away from this shot it certainly warrants our consideration.
Another thing to consider about a boiling mirage is this. If you look at your target and see right to left or left to right movement but can't really decern wind direction, turn your scope right or left until you see a boiling mirage. That will be the direction the wind is blowing.
Watching the mirage move from right to left or left to right is what the marksman is looking for when doping for windage. Generally, when we consider doping for wind, it has to do with moving the bullet from off center, to center. The slant of the mirage's waves will provide information about velocity as well as direction. The greater the slant the faster the wind.
When you see the lines of the mirage horizontal and straight you have a really good wind, usually twenty plus miles per hour. This is an extremely poor condition to deliver a shot in. Also keep in mind that when you have this type of wind, even of lesser velocity, the target will be distorted in the direction the wind is moving. The target will be left, or right, of where you think it is.
If you have a bright, sunny, day and distortion surrounds your target, watch the mirage. You will see it elongate the target. If the wind is blowing from left to right you will see the right side of the target get bigger. This area of the target will appear to swell in the direction the mirage is moving. If the swelling of the area appears to pulsate, that means the wind is intermittent. Again, these effects increase with distance.
There are some relatively new instruments on the market to measure wind velocity. Here are some things to think about.
a. It tells you wind speed where you are. You really need to know
wind speed about halfway between you and your target.
b. The instrument generally reads the highest velocity. It does not
provide information on lulls, changes, and buildup.
c. It cannot always detect direction of wind.
As a piece of equipment, the wind gauge, should be used in conjunction with your observations. Do not use it as an exclusive measurement. Simply factor the information obtained with other information. Your location will be the key factor in determining its usefulness, and sometimes it will be more useful than others.
Where I see this tool at its best is in training. Read the mirage off a location at a midway point down range. Then go down and check it with the instrument. See how close you are. Don't be dismayed to have four or five instruments of the same manufacturer give you that many readings, but they should be consistent with themselves. So learning your dope with the instrument should provide consistency with what you get as a reading and what you see in your scope. Give it a try.
As an aside, I have had people tell me, "I don't have anything downrange I can read". If this is the case, or if there is some range rule that prohibits placing something there, use a piece of tar paper. For you roofers, this is "felt", I know, but rifle guys are a technical bunch. I haven't found anyone yet who will object to placing a piece of tar paper on the ground, maybe three or four feet square, put a little dirt on the edges so it won't blow away.
This will provide you with a common spotting location and is an excellent tool to train people to dope.
Judging wind velocity by mirage movement is an art form. Nobody I know of, who is knowledgeable, will tell you it is an exact science or that it has exacting qualities. The ability to read mirage comes with experience. There is just no other way to learn it well enough to make that critical shot.
The other key factor in doping is knowing your equipment. Just because your department has a thousand dollars invested in a rifle scope, doesn't mean you get a quarter minute click when you turn the adjustment knob. That may be what you are supposed to get, but it rarely is. You will not know until you get out and try it. People who know their equipment know this is true, the rest of you will learn soon.
When you're doping, don't just assume that you made a mistake in application of the dope. Draw a picture of what your read looks like so that it is comparable at another time. Identify reads that are similar. Check to see if the same dope applies consistently. This is how you collect real dope. "I have seen this before, this is what I did, and this is how it works." This information is priceless to the marksman who needs to make the shot count.
You cannot count this information as pure fact. Weather conditions change as well as the condition of your gun and maybe a new lot number of ammunition has been thrown in. Never discount the variables. Look out for false mirage, reflections of mirage itself, and make sure what you are looking at is real. Even long time shooters can be fooled, this is evidence you have to work at your craft.
The major reason the tactical shooter should dope from mirage readings is the fact that wind change can be detected immediately.
Suggestions to Improve Your Ability
a. Alter your shooting schedule any time you can. Don't go to the range at the same time of day.
b. Shoot on different ranges whenever possible.
c. Shoot in a variety of weather conditions, don't just go out on sunny days. A little rain may impress you as to what it will do. Do we still work in the rain?
d. Zeros are a funny thing. Many times we shoot from sand bags or other supported positions, rests and bipods and the like, obtain a zero and the next time we shoot off something else and wonder why our zero changed. The only place to zero is in the position and condition you are going to employ it.
Example; I shoot three clicks difference from standing to sitting, two clicks different from sitting to prone, and two clicks different from sitting to supported kneeling. What I do off a bench or bipod is two to five clicks off from all other positions. Check it out.
e. Make sure you record, keep and review your data. Constantly
compare your new efforts with previous recordings. By review you will learn things about your rifle. Change with it and rebarrel it when it's time.
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