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Definitions for Rifle Work

 

Line of Sight is a straight line between the eye and the target that runs through the rifle’s sight system.

Iron Sights use a front sight composed of a bead or post near the rifle’s muzzle.  Since the eye can only focus clearly upon a single object, it is the front sight that demands the ultimate and final concentration of focus.  The rear sight is typically either a notched blade mounted at the rear of the barrel or a disk with a peep hole mounted at the rear of the receiver and closer to the shooter’s eye. Iron sights are generally only ¾ inch above the bore.

 

Sight Radius is the distance between the front and rear sights.  The longer the sight radius, the less visual error will be accentuated during alignment.

 

Sight Alignment occurs when the top of the front sight is level with the top of the rear sight and the blade is centered as the eye looks through the notch.  The eye automatically centers the front bead though the peep hole of the receiver sight to make good use of the longer sight radius.  Small peeps may be more accurate, but larger holes, or Ghost Rings, are faster to use in less ambient light.  Sights may be painted for more contrast, fitted with light gathering fiber optic tubes which may tire the eye in a prolonged view, or fitted with small self luminous tritium gas tubes that glow in the dark without needing batteries.

 

Sight Picture refers to what the eye sees when the sights are aligned on a target.  Remember to focus on the front sight just as the shot breaks.  Insure that no intervening obstacles or brush will deflect the bullet, and that the background does not preclude shooting.  Any misalignment of the sights will be amplified as distance increases, but at close range, fast follow up shots can be made with a Flash Sight picture when the front sight is anywhere in the notch or peep.  In extremely close quarters, the rifle can be swung and pointed at the target without acquiring the sights at all.

 

 

Windage and Elevation corrections to iron sights are typically made to the rear sight, back and forth and up and down.  Move the rear sight left to shift bullet impact to the left.  Move the rear sight up for more muzzle elevation to raise the point of impact.  However, moving the front sight produces the opposite effect.  When the point of impact at a certain distance is satisfactory, the rifle is said to be Zeroed In at that range.

 

Telescopic, Red Dot, and Holographic sight systems all place the target and sight in the same focal plane, so the eye can concentrate on the total sight picture.  Intermediate brush can disappear in a scope.  Optics are generally 1 ½ inches above the bore axis.  A high power scope has a narrow Field of View that makes it harder to pick up or follow moving targets without practice.  A lower power scope is faster to use, and it doesn’t flaunt the jitters and compromise the shooter’s confidence.

 

Eye Relief is the optimal distance from the eye to the scope’s Eyepiece.  Under the heavy recoil of a rifle held loosely, the eyepiece can cloud a shooter’s vision with blood running down from the circle cut in the brow.

Parallax is an error inherent in optical sights and misalignment of the eye with the axis of the scope.  Some scopes allow a correction for this near the front Objective Lens.  Fortunately, most low power Red Dot and Holographic sights are free from errors in Eye Relief and Parallax, which lend them well to fast, close engagement.

 

Exit Pupil of a scope is the diameter of the light beam coming from the eyepiece, which can be seen by holding the scope at arms length.  The eye’s pupil, on the other hand, changes according to ambient light.  In bright light, a pupil constricts so much, to about 1mm, that most of the scope’s light beam doesn’t even get to enter the eye.  In very low light, a pupil dilates so much, to about 5mm, that the eye has to search around for the scope’s exit pupil, because now it seems too small. The diameter of the exit pupil is determined by the objective lens diameter divided by the scopes magnification power.  For example, a 3-9 variable power scope with a 42mm objective will have plenty of exit pupil with 14mm at 3 power (42/3), and 4.67mm at 9 power (42/9).  A 10 power scope with a 56mm objective will produce a 5.6mm exit pupil (56/10), excellent for very low light situations, especially if the reticle is illuminated.  But it would be heavy and need to be mounted high off the bore to clear the objective bell.

 

Reticles are the systems of fine wires or visual displays seen by the eye when sighting through an optical device.  A crosshair or single dot is simple.  There are more elaborate reticles allowing range and elevation estimation.  Some are battery powered, some are self illuminating, and some systems piggyback close quarter units on top of, or along side of longer range sights.  Windage and elevation adjustments are typically made by removing protective caps and turning dials with clicks for precise angular changes.

 

Angular Measurement is at the heart of marksmanship.  

 

1.  The Minute of Angle or MOA

 

The rifleman is at the center of two circles, surrounding him horizontally and vertically.  A circle has 360 degrees, and each degree has 60 minutes, so there are 21,600 minutes of angle all around.  The formula to determine circumference is 2 times the radius times PI (3.14159…).  And if the circumference of a large circle is 21,600 inches, each inch at the edge represents one MOA.  It so happens that a circle that large has a radius of nearly 100 yards.  The rifleman is in the center of the circle and approximately 100 yards from the edge.  If the rifleman is 200 yards from the edge, a MOA equals approximately 2 inches, at 350 yards, a MOA is 3.5 inches, and at 1000 yards, a MOA is 10 inches (10.47 inches to be exact or 1000yds X 36” X 2 X pi  / 21600).  If the rifleman knows the distance to the target, he can calculate how many inches are in each MOA and use the clicks of his scope adjusters to zero in elevation and windage.

 

2.  The Mil Dot Reticle

 

This is a simple crosshair with small dots on the two fine hairs spaced 1 MIL apart.  The mil is a metric term for 1 in a thousand.  For example, there are 1000 milliliters in a liter.  For the purpose of angular measurement, a MIL is 1/1000 of the range.  There are 6283 MILs in a circle.  The US Army artillery uses 6400 MILs in a circle, but the difference is slight.  At 100 yards (or 3600 inches) a MIL is 3.6 inches.  At 1000 yards, a MIL is one yard.   At 2 kilometers, a MIL is 2 meters.  If the rifleman knows the distance to the target, he can calculate how many inches are in each MIL and use the mil dots on the reticle to aim, instead of twisting scope adjusters.  In addition, when the size of the target is known, and its mil size through the scope is observed, the distance can be very accurately estimated.  For example, a 6 foot man (or 2 yards tall) will be covered by 2 MILs at 1000 yards, or 4 MILs at 500 yards, or 10 MILs at 200 yards.  A free demo tutorial on mil dot rangefinding can be found at:

 

htp://www.shooterready.com/lrsdemo.html

 

The full software package is worth obtaining.  Sierra’s ballistic software, INFINITY, is also a worthwhile investment that can graph the curve of a bullet’s path.  Perhaps using a laser rangefinder would be slightly more accurate, but its signature will give away the rifleman’s position to a sophisticated adversary.

 

A Rifleman knows where his bullet is at any distance.

 

Bullet Path is the curve that a bullet follows after it leaves a horizontal rifle bore and is subjected to air resistance drag, temperature, altitude, humidity, wind, and most of all, gravity.  For practical purposes, only gravity and wind will be considered here.  Ballistic Coefficient (BC) is a number given to a bullet that compares how well it slips through the air, generally from .100 to .600, the higher the better.  Sectional Density is a measure of how long and heavy the bullet is to punch its way through.  High sectional density, a pointed tip, and a tapered boat tail all increase the BC.  The BC will change slightly as velocity drops, and the shock crossing the sound barrier (about 1100 feet per second) can alter its path.  Bullet manufacturers will publish tables that list BC, drop, and drift for different muzzle velocities and distances.  Cartridge manufacturers will give charts with this information for their different offerings, too.  Once the rifleman finds the cartridge or load that his rifle likes best, he will fire at different ranges and note the actual points of impact and group sizes in order to compile a trajectory table.  In general, all rifles will shoot flat with tight groups for awhile, but then they all drop like a rock due to gravity as distance and time of flight increases.   No matter what old timer or super magnumated round you use, it is important to make graphs of the curves of bullet drop as well as wind drift for extended ranges.

 

Trajectory is the measure of bullet path in relation to the line of sight.  A straight ruler can be used to represent the line of sight when it is placed on the bullet drop graph.  Pin one end of the ruler at zero yards so it rests about 1½ inches above the starting point of the bullet, if the rifle is scoped, or ¾ inch high if iron sighted.  The distance between the bore and the sights is called the sight Offset, and a lot of offset can cause problems in close quarter shooting.  Rotate the other end of the ruler down or pivot the graph up, so that the curved bullet path crosses the straight edge.  As the bullet rises from the muzzle, it crosses the ruler at very close range, rises above, and then crosses again as it falls to the zeroed in range.  After that, the trajectory will start falling rapidly and require considerable hold over.   Pivoting the graph will show where the bullet is for different zeroes, and the rifleman must choose a distance for his best general purpose.  A moderate range zero allows the flat bullet drop section of the graph to nearly correspond with the line of sight for quite some distance.  A long range zero will require some mid range hold under, because the trajectory has to rise more before it falls back to the line of sight at the zero range.

 

 

 

Creating a Shooting Table for the Field

 

After the zeroed in distance has been selected, draw a straight line of sight on the graph, starting with the sight offset at the muzzle and crossing the bullet path at the zero distance.  Straighten the graph so the line of sight points down at an angle and the bullet path starts out horizontally.  Measure in inches the trajectory, above or below the line of sight, at numerous points.  Convert each point to a plus or minus MOA for rotating scope adjusters.  Or convert each point to a plus or minus MIL for using a mil dot scope. Create a companion windage chart or graph, and tape them to the rifle stock for reference.  Make sure your eyes can read the fine print.  A photographic memory is helpful if you shoot different bullet weights or rifles.

 

Distance      Trajectory              Wind Drift

Yards          Mils or MOA         Mils or MOA

25                …                         …              

50                …                         …

75                …                         …

100              …                         …

125              …                         …

….              …                         …

….              …                         …

975              …                         …

1000            …                         …

 

This blank table is an example of listing information important to long range marksmanship.  

 

Shooting at Vertical Angles

 

A target that is either high or low is not as far away from the rifle as it looks to the eye or line of sight.  The actual distance for which a correction must be made is only the horizontal component of the range.  Imagine the target were to be raised or lowered to the shooter’s horizon and use that shorter range.  Knowing the exact visual distance and angle from horizontal, the trigonometric cosine of the angle times the visual distance will yield the true “rifle” range.

Doping the Wind

 

A head wind or tail wind will have little or no effect on trajectory, but a cross wind is important to correct.  When a wind comes or goes from an angle, only the cross wind component requires correction.  It can also be calculated using trigonometry.  The effective crosswind component is the sine of the angle times the actual wind speed.  Mid range winds and gusts can test even the best of marksmen.

 

Hold Your Breath

 

As you perfect the final sight picture, oxygenate the blood with several deep breaths.  Then release about 10% - 20% of the last full breath while leaving the airway open.  It's going to take a strong psychology to isolate your mind and body distractions from the need for total concentration.  Now time your heartbeat with the movement of the sight picture and release the rifle’s striker just as the sight alignment swings to target.  It may take some practice learning how to roll up the trigger using snap caps instead of live ammunition.  Release the striker without anticipating the click or disturbing the sight picture.  It’s good to have a light, crisp trigger, free of Creep, Stacking, and Over Travel, with a fast Lock Time between release and ignition.  Right after the shot, avoid the temptation to try to see what you did to the target, because that can spoil your follow through.  Respect the man with one rifle who can manage his trigger.

 

Like a Rock

 

From a bench rest, a rifle will exhibit its inherent capabilities.  Does the first shot from a clean, cold barrel have a different point of impact?  Does the point of impact change as the barrel heats up?  Does the humidity or temperature affect the wood stock?  Synthetic and laminated wood stocks are the most stable.  Getting tight, consistent groups from the bench is fundamental.  Shooting in the field from different positions, using the sling, bipod, or improvised rests, will reveal improvements in your skill and the different range limits that a sportsman will not exceed.  A challenge to your cool steadiness would be to shoot under heart pounding stress or after exertion.

 

Standing (offhand), Kneeling, Sitting, and Prone are the principal positions to learn.  The more contact with the ground, the steadier the position, but don’t allow the rifle itself to contact a hard object.  Start each position by finding the natural point of aim.  Study the basics of each position and find the posture that relieves the most muscle tension.  Close the eyes and aim.  Open the eyes and adjust the body so that the natural point of aim is on target.  Use the sling in the kneeling and sitting positions.  A two point sling with easy adjustment is best.  Use a bipod or knapsack as a rest when available.

 

Citizen Marksman

 

Drop the membership in the health club.  Use the weight of the rifle and extra ammunition for “rifle aerobics.”  Learn about combat breathing, trauma care, Israeli Battle Dressings, and make first aid kits for home and cars.  Develop survival plans, like your fire drills, keep your gas tanks full, and your pantry stocked.  Have a “bug out bag” to grab in a hurry.  Then relax in peace.  You and your family will be survivors when others perish, unprepared for sudden emergencies.

 

Read the Declaration of Independence, the US Constitution, and the writings of the founding fathers.  Keep up with current affairs from diverse sources, and then be sure to let your family, friends, and elected representatives know your opinions.  VOTE as if the future of your grandchildren depend on it

 

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