Point Blank
The concept of a “point blank” zero is to sight in your rifle to take best advantage of the ballistic curve in combination with the height of your sights above the boreline to eliminate the need to hold over your target at the maximum possible range. While sound in theory (the difference between practice and theory is much greater in practice than in theory) there are some problems with a point blank zero as usually executed.
The line of sight through your rifle sights is a straight line. Your bullet travels in a curve as determined by the angle of departure and gravity. If the sights and bore were parallel to each other and the ground (horizontal), when you fired your rifle the bullet would begin dropping toward earth at an acceleration of 32 feet per second per second (one gravity) beginning it’s trajectory a distance below the sights equal to their height above the bore and moving farther away from the sightline until it struck the ground. When you sight in or zero a rifle you angle the barrel upward so that the ballistic curve touches or crosses the sight line. With most zeros the bullet will cross the sightline once fairly close to the muzzle (less than 50 yards) on the way up, and then cross it again farther out (usually a few hundred yards) on the way down.
Given the size of the target you are trying to hit- say the generally accepted 10 inch diameter heart/lung kill zone of a deer- the idea is to sight in your rifle so that the bullets path neither rises above nor falls below the sightline more than one-half the diameter of your target- 5 inches on our imaginary deer.
Since I’m playing with an AR15 right now, I’ll use it for my examples.
The iron sights on my AR are 2 ½ inches above the bore; this is considerably higher than what you’ll find on most sporting rifles which are generally about an inch and a half above the bore. The bullet will start 2 ½ inches below the sightline. With a 300 meter zero and M855 ammunition, the bullet will rise to meet the sightline at about 30 meters. The bullet will continue to rise until it reaches 3.75 inches above the sightline at a range of 180 meters and then it will begin to fall back to earth. The bullet will cross the sightline again at 300 meters. At 335 meters it will again be 2 ½ inches below the sightline and at 345 meters it will fall 3.75 inches below the sightline. This means that by zeroing my rifle at 300 meters I have a theoretical point blank range of 345 meters for a target of 7.5 inches diameter where my bullet path doesn’t travel more than 3.75 inches above or below my line of sight. I should be able to aim directly at the center of a 7.5 inch target and place my bullet somewhere on it out to 345 meters without worrying about holdover. At least, that’s the theory.
Reality introduces some variables that aren’t taken into account by most point blank theorists.
First is the target. I find that most people allow for a much larger target than is realistic to expect. Let’s take that 10 inch target on a deer. Ten inches cover just about the entire broadside chest area on a fairly large whitetail. A smaller whitetail or one standing at an angle or with a partially obscured kill zone will present a smaller target. Also, a hit anywhere in that 10 inch circle may not be a good hit. Hits low and back in the lungs may not be fatal. A hit in the lungs with a bullet that fails to expand may not be fatal (or may be fatal after the deer runs onto the nearby Indian reservation where I don’t have a permit). A bullet that expands beautifully at close range may have lost too much velocity at the outer limits of the point blank range to expand reliably; this means that right where the bullet is striking low in the lungs and most needs to expand it has the least chance to expand.
Let’s limit the kill zone to structures that are most likely to be damaged by a bullet that fails to expand explosively- say, the heart and associated blood vessels. Suddenly our target has shrunk from 8 or 10 inches to only 3 or 4.
In the antipersonnel role a 7.5 inch center mass target may seem reasonable. On an exposed stationary target that’s facing you 7.5 inches may be reasonable. But what if your target is turned sideways or all you can see is the top of his pointed little head peaking out from behind some sandbags?
The next problem is group dispersion. How large a group are you shooting at your maximum point blank range? On a good day from a field rest with iron sights the best that I can expect is only 1 ½ minutes of angle. The AR15 with M855 ammo is usually only good for 1 ½ to 2 minutes of angle. At 345 meters that means that the best group I can expect is about 6 inches, and under actual field conditions I’ll be lucky to get that. That means that at 345 meters my bullets may strike anywhere within 3 inches of my intended strike point. At 345 meters my intended strike point is going to be at the bottom of my 7.5 inch point blank target. My actual bullet strike may end up three inches below my 7.5 inch target. At 180 meters my optimistic group size will be three inches which allows for a potential bullet strike 1 ½ inches above my target. These are optimistic estimates; things could get worse. Of course you can always depend on luck to put your bullet on the other side of your group and send it closer to the center of your target. Luck always works, right?
A third problem is range estimation. This is usually more of a problem with hunters hunting unfamiliar game or areas. I find that most hunters overestimate the range by almost 50 percent. For example, in Wisconsin the vast majority of hunters that came to the shop to have me sight-in their rifles would complain that the 100 yard bench was much farther than 100 yards. The fact that we had the range surveyed with a laser transit didn’t phase these guys. I used to ask them where they thought the 100 yard mark was and they were amazingly consistent at placing it at 60 yards. Now, move these same guys from low altitude, high humidity Wisconsin to the Rocky Mountains where the thin, dry air makes the game look closer but the low plant life makes the range look longer to begin with, and you see some extreme overestimates. The guys coming back from Wyoming or Colorado would consistently call 150 to 200 yards 400 yards or longer. This observation is backed by the opinions of numerous western hunting guides.
Let’s take our midwestern whitetail hunter and put him in eastern Colorado hunting pronghorns. He has his fancy, high-steppin’ magnum sighted in for a maximum point blank of 450 yards. He sees a pronghorn and estimates the range at 400 yards. The pronghorn is smaller in the body than the whitetails he’s used to, the atmosphere is clearer than he’s used to, the scrub is lower than he’s used to, and he’s an inexperienced judge of range anyway (probably never having seen more than 200 yards of range in the Wisconsin timber) so the animal is only 200 yards away- very close to the maximum ordinate of his bullet’s trajectory. Now even 200 yards is about five times as far as this fellow has ever shot a large animal in the northern woods. Intellectually he knows that he’s supposed to be able to aim dead on out to 450 yards but that animal looks so much smaller and farther away than anything he’s ever hunted that he instinctively holds a little high. Now our intrepid Nimrod (note that “Nimrod” is not an insult and means an enthusiastic hunter) is holding a bit high on an animal he has estimated to be 400 yards away but is really half that. On top of that, his shot strikes a little high in his rather generous wobble area. What should be a 200 yard clout shot with a high-velocity cartridge ends up a clean miss high. This is a very typical scenario as described by several guides here and in Africa. Ross Seyfried went so far as to insist that all his clients zero their rifles for a 4 inch kill zone- the bullet doesn’t travel more than two inches above or below the sightline. A 4 inch kill zone gives about a 200 to 220 yard zero and a 250 yard point blank with most high-velocity cartridges.
One other problem with a long range zero is the height of the trajectory curve makes canting the rifle more of a consideration. The higher the sights or the larger the maximum ordinate of the ballistic curve the more effect canting the rifle will have. At close ranges canting has little effect. As ranges get longer or the trajectory gets steeper a cant of only a few degrees from vertical can have a great effect on windage and a lesser effect on elevation.
Efforts to maximize the point blank range include choosing cartridges for a flat trajectory and mounting the sighting system higher above the bore.
Flattening the trajectory is possible by increasing velocity or ballistic coefficient. Too often a flat trajectory is attempted by using lightweight projectiles that give a nice flat curve at close range but lose velocity more rapidly at longer ranges than a heavier projectile. A light bullet also gives up terminal effect with less penetration and a greater chance of bullet failure.
Higher sights have no effect on the trajectory but give the illusion of a longer point blank. A 2 ½ inch high sight when zeroed at 100 yards will be striking 1 inch higher in relation to the muzzle than a 1 ½ inch high sight zeroed at the same distance. Higher sights also have the attendant problems with canting and handling characteristics.
I find a reasonable close range point blank zero to be one that allows for a target that is double the height of the sights. This means a 3 to 4 inch target for most sporting rifles and a 5 inch target for the AR15 or a rifle with see through mounts. With the AR15 a 5 inch kill zone gives a 50 meter near zero, a 200 meter zero and about a 250 meter point blank. For the AR15A2 sights I go ahead and use a 300 meter zero with the long range aperture so that the rear sight is calibrated correctly.
If you use longer range zeros you must know your trajectory intimately. Remember that the maximum ordinate (height above the sightline) will be approximately 2/3 of the distance to your zero- not halfway. If you sight-in your .270 about 1 ½ inches high at one hundred yards it will be around two inches high at 150 yards and zeroed at 200.
The concept of a “point blank” zero is to sight in your rifle to take best advantage of the ballistic curve in combination with the height of your sights above the boreline to eliminate the need to hold over your target at the maximum possible range. While sound in theory (the difference between practice and theory is much greater in practice than in theory) there are some problems with a point blank zero as usually executed.
The line of sight through your rifle sights is a straight line. Your bullet travels in a curve as determined by the angle of departure and gravity. If the sights and bore were parallel to each other and the ground (horizontal), when you fired your rifle the bullet would begin dropping toward earth at an acceleration of 32 feet per second per second (one gravity) beginning it’s trajectory a distance below the sights equal to their height above the bore and moving farther away from the sightline until it struck the ground. When you sight in or zero a rifle you angle the barrel upward so that the ballistic curve touches or crosses the sight line. With most zeros the bullet will cross the sightline once fairly close to the muzzle (less than 50 yards) on the way up, and then cross it again farther out (usually a few hundred yards) on the way down.
Given the size of the target you are trying to hit- say the generally accepted 10 inch diameter heart/lung kill zone of a deer- the idea is to sight in your rifle so that the bullets path neither rises above nor falls below the sightline more than one-half the diameter of your target- 5 inches on our imaginary deer.
Since I’m playing with an AR15 right now, I’ll use it for my examples.
The iron sights on my AR are 2 ½ inches above the bore; this is considerably higher than what you’ll find on most sporting rifles which are generally about an inch and a half above the bore. The bullet will start 2 ½ inches below the sightline. With a 300 meter zero and M855 ammunition, the bullet will rise to meet the sightline at about 30 meters. The bullet will continue to rise until it reaches 3.75 inches above the sightline at a range of 180 meters and then it will begin to fall back to earth. The bullet will cross the sightline again at 300 meters. At 335 meters it will again be 2 ½ inches below the sightline and at 345 meters it will fall 3.75 inches below the sightline. This means that by zeroing my rifle at 300 meters I have a theoretical point blank range of 345 meters for a target of 7.5 inches diameter where my bullet path doesn’t travel more than 3.75 inches above or below my line of sight. I should be able to aim directly at the center of a 7.5 inch target and place my bullet somewhere on it out to 345 meters without worrying about holdover. At least, that’s the theory.
Reality introduces some variables that aren’t taken into account by most point blank theorists.
First is the target. I find that most people allow for a much larger target than is realistic to expect. Let’s take that 10 inch target on a deer. Ten inches cover just about the entire broadside chest area on a fairly large whitetail. A smaller whitetail or one standing at an angle or with a partially obscured kill zone will present a smaller target. Also, a hit anywhere in that 10 inch circle may not be a good hit. Hits low and back in the lungs may not be fatal. A hit in the lungs with a bullet that fails to expand may not be fatal (or may be fatal after the deer runs onto the nearby Indian reservation where I don’t have a permit). A bullet that expands beautifully at close range may have lost too much velocity at the outer limits of the point blank range to expand reliably; this means that right where the bullet is striking low in the lungs and most needs to expand it has the least chance to expand.
Let’s limit the kill zone to structures that are most likely to be damaged by a bullet that fails to expand explosively- say, the heart and associated blood vessels. Suddenly our target has shrunk from 8 or 10 inches to only 3 or 4.
In the antipersonnel role a 7.5 inch center mass target may seem reasonable. On an exposed stationary target that’s facing you 7.5 inches may be reasonable. But what if your target is turned sideways or all you can see is the top of his pointed little head peaking out from behind some sandbags?
The next problem is group dispersion. How large a group are you shooting at your maximum point blank range? On a good day from a field rest with iron sights the best that I can expect is only 1 ½ minutes of angle. The AR15 with M855 ammo is usually only good for 1 ½ to 2 minutes of angle. At 345 meters that means that the best group I can expect is about 6 inches, and under actual field conditions I’ll be lucky to get that. That means that at 345 meters my bullets may strike anywhere within 3 inches of my intended strike point. At 345 meters my intended strike point is going to be at the bottom of my 7.5 inch point blank target. My actual bullet strike may end up three inches below my 7.5 inch target. At 180 meters my optimistic group size will be three inches which allows for a potential bullet strike 1 ½ inches above my target. These are optimistic estimates; things could get worse. Of course you can always depend on luck to put your bullet on the other side of your group and send it closer to the center of your target. Luck always works, right?
A third problem is range estimation. This is usually more of a problem with hunters hunting unfamiliar game or areas. I find that most hunters overestimate the range by almost 50 percent. For example, in Wisconsin the vast majority of hunters that came to the shop to have me sight-in their rifles would complain that the 100 yard bench was much farther than 100 yards. The fact that we had the range surveyed with a laser transit didn’t phase these guys. I used to ask them where they thought the 100 yard mark was and they were amazingly consistent at placing it at 60 yards. Now, move these same guys from low altitude, high humidity Wisconsin to the Rocky Mountains where the thin, dry air makes the game look closer but the low plant life makes the range look longer to begin with, and you see some extreme overestimates. The guys coming back from Wyoming or Colorado would consistently call 150 to 200 yards 400 yards or longer. This observation is backed by the opinions of numerous western hunting guides.
Let’s take our midwestern whitetail hunter and put him in eastern Colorado hunting pronghorns. He has his fancy, high-steppin’ magnum sighted in for a maximum point blank of 450 yards. He sees a pronghorn and estimates the range at 400 yards. The pronghorn is smaller in the body than the whitetails he’s used to, the atmosphere is clearer than he’s used to, the scrub is lower than he’s used to, and he’s an inexperienced judge of range anyway (probably never having seen more than 200 yards of range in the Wisconsin timber) so the animal is only 200 yards away- very close to the maximum ordinate of his bullet’s trajectory. Now even 200 yards is about five times as far as this fellow has ever shot a large animal in the northern woods. Intellectually he knows that he’s supposed to be able to aim dead on out to 450 yards but that animal looks so much smaller and farther away than anything he’s ever hunted that he instinctively holds a little high. Now our intrepid Nimrod (note that “Nimrod” is not an insult and means an enthusiastic hunter) is holding a bit high on an animal he has estimated to be 400 yards away but is really half that. On top of that, his shot strikes a little high in his rather generous wobble area. What should be a 200 yard clout shot with a high-velocity cartridge ends up a clean miss high. This is a very typical scenario as described by several guides here and in Africa. Ross Seyfried went so far as to insist that all his clients zero their rifles for a 4 inch kill zone- the bullet doesn’t travel more than two inches above or below the sightline. A 4 inch kill zone gives about a 200 to 220 yard zero and a 250 yard point blank with most high-velocity cartridges.
One other problem with a long range zero is the height of the trajectory curve makes canting the rifle more of a consideration. The higher the sights or the larger the maximum ordinate of the ballistic curve the more effect canting the rifle will have. At close ranges canting has little effect. As ranges get longer or the trajectory gets steeper a cant of only a few degrees from vertical can have a great effect on windage and a lesser effect on elevation.
Efforts to maximize the point blank range include choosing cartridges for a flat trajectory and mounting the sighting system higher above the bore.
Flattening the trajectory is possible by increasing velocity or ballistic coefficient. Too often a flat trajectory is attempted by using lightweight projectiles that give a nice flat curve at close range but lose velocity more rapidly at longer ranges than a heavier projectile. A light bullet also gives up terminal effect with less penetration and a greater chance of bullet failure.
Higher sights have no effect on the trajectory but give the illusion of a longer point blank. A 2 ½ inch high sight when zeroed at 100 yards will be striking 1 inch higher in relation to the muzzle than a 1 ½ inch high sight zeroed at the same distance. Higher sights also have the attendant problems with canting and handling characteristics.
I find a reasonable close range point blank zero to be one that allows for a target that is double the height of the sights. This means a 3 to 4 inch target for most sporting rifles and a 5 inch target for the AR15 or a rifle with see through mounts. With the AR15 a 5 inch kill zone gives a 50 meter near zero, a 200 meter zero and about a 250 meter point blank. For the AR15A2 sights I go ahead and use a 300 meter zero with the long range aperture so that the rear sight is calibrated correctly.
If you use longer range zeros you must know your trajectory intimately. Remember that the maximum ordinate (height above the sightline) will be approximately 2/3 of the distance to your zero- not halfway. If you sight-in your .270 about 1 ½ inches high at one hundred yards it will be around two inches high at 150 yards and zeroed at 200.
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