External Ballistics: External ballistics pertains to bullet velocity, energy and trajectory down-range. Bullet trajectory is the flight path of the bullet relative to some known and fixed points. Bullet Trajectory And Sighting Plane: 1. Point blank range when sighting in a rifle is the first point at which the line of sight intersects with the bullets path in the bullets trajectory. 2. Mid-range rise when sighting in a rifle is the highest point in the bullets trajectory between the point blank range and true zero. 3. True zero when sighting in a rifle is the second point at which the line of sight intersects with the bullets path in the bullets trajectory. 4. Maximum point blank range when sighting in a rifle is the height of the mid-range rise and the bullet drop beyond true zero, both are equal in measure.
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Rifle Sight Height And Bullet Trajectory: To properly sight-in a hunting rifle a person needs to know a little bit about their scope mount height of their rifle as this affects the sight plane that intersects with the bullet's trajectory.
Rifle Sight Height to Bore Center Line: Open Sights = 1 inch sight height.
Rifle Scope Center Line to Bore Center Line: Low Scope Mount And Rings = 1.5 inch sight height. Medium Scope Mount And Rings = 1.8 inch sight height. High Scope Mount And Rings = 2.0 inch sight height. Rifle Barrel Length, Bullet Velocity And Energy: Bullet velocity readings are generally taken from a rifle barrel length of 24 inches and using the following formula the bullets energy is determined; velocity x velocity x bullet weight = _ divided by 450,340 = bullet kinetic energy in foot pounds. If your rifle barrel length is not 24 inches then you have to recalculate the bullet velocity and bullet energy. Rifle Barrel Length Shorter Than 24 Inch You Subtract Velocity. Rifle Barrel Length Longer Than 24 Inch You Add Velocity. 2,500 to 3,000 feet per second advertised velocity, adjust at 20 feet per second per inch from standard of 24 inch rifle barrel. 3,000 to 3,500 feet per second advertised velocity, adjust at 30 feet per second per inch from standard of 24 inch rifle barrel. 3,500 to 4,000 feet per second advertised velocity, adjust at 40 feet per second per inch from standard of 24 inch rifle barrel. Bullet Ballistic Coefficient: The bullet ballistic coefficient, higher B.C.s mean flatter trajectories and higher retained energy down-range on target. A ballistic coefficient is the measure of a bullet's relative ability to overcome air resistance. Each bullet is assigned a numerical value expressing this efficiency. Ballistic coefficient calculations combine both shape and sectional density factors. Bullet Sectional Density: Bullet sectional density is a mathematical factor expressing the relationship between the weight of the bullet and its cross-sectional area. Sectional density best describes a bullet’s length as to its diameter, the higher the number, the longer the bullet. Generally speaking, longer bullet’s of a given diameter (high S.D.) will penetrate deeper than will shorter bullet’s of the same given diamter (low S.D.). Having said that, bullet construction ultimately determines its usage for hunting, always follow recommendations by the manufacturer. Bullet Energy: Before the bullet is down-range and on target, you have to know whether the bullet will have enough energy retention to cleanly harvest the animal. A bullet's kinetic energy is measured in foot pounds, and this is a proxy for what's generally termed stopping-power. The higher a bullet's energy at the point of impact, the greater its stopping-power. Bullet Impact Zone: Just as important is the size of target that a game animal that your hunting presents to you, typically standing broadside, exposing heart and lung area. Moose Size Game Hunting:
Bears Moose These animals are quite large and offer about an eight inch target zone, for a correct rifle sight-in, a four inch mid-range is required for minimum bullet trajectory effect. For this size animal, I prefer 2,000 foot pounds of bullet energy. Elk Size Game Hunting:
Caribou Sheep Elk These animals can be quite large and offer about an six inch target zone, for a correct rifle sight-in, a three inch mid-range is required for minimum bullet trajectory effect. For this size animal, I prefer 1,800 foot pounds of bullet energy. Deer Size Game Hunting:
Antelope Blacktail Deer Hogs Javelina Mule Deer Whitetail Deer These animals can be somewhat small at times and offer about an four inch target zone, for a correct rifle sight-in, a two inch mid-range is required for minimum bullet trajectory effect. For this size animal, I prefer 1,200 foot pounds of bullet energy. Predator Hunting:
Bobcat Cougar Coyote These animals can be somewhat small and offer about an two inch target zone, for a correct rifle sight-in, a one inch mid-range is required for minimum bullet trajectory effect. For this size animal, I prefer 360 foot pounds of bullet energy. Hunting Rifle Sight-In Procedure: 1. At exactly 50 yards put up a target that you can clearly see with your sight system. A. For a air-rifle of reasonable power, 50 yards will most likely be the furthest maximum point blank range in the trajectory path for sighting in purposes. B. For a rimfire rifle, 50 yards will most likely be the true zero point in the trajectory path for sighting in purposes. C. For a muzzleloading rifle, 50 yards will most likely be the mid range rise in the trajectory path for sighting in purposes. D. For a centerfire rifle, 50 yards will most likely be the point blank range in the trajectory path for sighting in purposes. 2. Now with your rifle properly rested on a rifle rest on top of a solid shooting bench, slowly and methodically fire three precise rounds. 3. Make an exact measurement from the center of your group to the center of your target make your windage adjustment accordingly, if you need to go left or right and you have windage adjustable scope bases, use the windage screws on the base, not the scope, rule of thumb for windage adjustment, if your bullet impact is to the left side of target loosen the right rear windage screw on the base and tighten the windage screw on the left rear side of the base. 4. Fire three more rounds to confirm your setting, if all is well and you have centered your group move on to step 5. If you are not satisfied with the accuracy of your ammunition at this point go no further until you have the ammunition you are happy with. 5. Depending on your rifle scope this is all you will be able to accurately do for this range outing, there are a lot of rifle scopes that do not like windage and elevation adjustments all at the same time. Any attempt to keep shooting with one of these scopes will only waste ammo and aggravate you to the point of despair. 6. Establishing a reference zero. A. Low powered air-rifles and small .22 rimfires, at exactly 50 yards zero your rifle. B. More powerful rimfires move out to exactly 75 yards and zero your rifle. C. 30/30 trajectory class centerfire rifles and muzzleloading rifles move out to exactly 100 yards and zero your rifle. D. High powered rifles move out to 100 yards and make sure your rifle is still center and a little high and then move on out to 200 yards and zero your rifle. 7. Trajectory plotting your rifle and ammunition combination for proper sight in. Class a and b rifles take your target and move it closer to you, firing 3 shot groups in 10 yard increments, mark the range on the target at each shot group. Class c and d rifles take your target and move it closer to you, firing 3 shot groups in 25 yard increments, mark the range on the target at each shot group. A. Continue moving the target closer to you until one group of shots emerges as the highest, this is confirmed when the next target move closer to you the grouping is lower. B. Congratulations riflemen at this point of the rifle sighting in procedure you have now established a true zero point and more importantly you have found the mid-range rise for your rifle, scope mounting, and ammunition selection. C. Now measure the center of your highest group on your target to your zero point, this is your true mid-range rise. D. Is this acceptable, or does it need to be adjusted for more or less rise. D. part 1. If the mid-range rise is to much, class a & b rifles move your target 10 yards closer, class c & d rifles move your target 25 yards closer to you from your original zero yardage and re-zero your rifle. Then repeat step 7 of the rifle sight-in procedure again. D. part 2. If the mid-range rise is not enough, class a & b rifles move your target 10 yards further, class c & d rifles move your target 25 yards further from your original zero yardage and re-zero your rifle. Then repeat step 7 of the rifle sight-in procedure again. Note: Repeat this procedure till you have exactly what you want. 8. Establishing your rifles maximum point blank range. Now that you have established your mid-range rise and your true zero, it's time for the final step in properly sighting in your rifle (M.P.B.R.). Class a and b rifles take your target and move it from your true zero point further from you, firing 3 shot groups in 10 yard increments, mark the range on the target at each shot group. Class c and d rifles take your target and move it from your true zero point further from you, firing 3 shot groups in 25 yard increments, mark the range on the target at each shot group. A. Continue moving the target further from you until one group of shots emerges as the same distance low as your mid-range high. Note: Example 2" high, 2" low. B. At this point of the rifle sighting in procedure you have now established a true zero point, you have found the mid-range rise and you have found your true maximum point blank range for your rifle, scope mounting, and ammunition selection. Your Rifle Is Now Properly Sighted-In. This is the only way to properly sight in a hunting rifle. |