Yes,
Bullet starts dropping as soon as it leaves the barrel if it shot level.
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Boresight, two lines that never meet
- Thread starter Redleg
- Start date
Bullet starts dropping as soon as it leaves the barrel if it shot level.
20 moa alters the angle on the line of displacement not the line of sight. The line of sight is the line that runs through the center of the scope to infinity and the line of bore is the line that runs through the bore to infinity. The difference between them is the height of the center of the scope above the center of the bore. In boresighting, this is the short leg (triangle) the long leg is the line of the bore with a target at 25 yards. They create a 90-degree angle. The line of sight will not move otherwise the scope height would have to be different every time you adjust the scope. From the line of sight, there is a line of displacement that offsets by the movement of the sight setting to get the crosshairs on the target at the end of the line of bore. The hypotenuse is the line of displacement that slopes downward to meet the line of bore. The line of sight and the line of bore run parallel and never meet. This is boresighting, not zero, no ballistics.
If the horizonal plane of the ground is your reference for level, then the only line that can be perpendicular to that to form a right triangle is the line that goes in front of the muzzle, straight up and down. That vertical line forms a 90 degree angle with the scope-view line, which is pointed at the target the same height above ground as the rifle is held.
Your rifle barrel (bore) will be aiming up, at some angle to be calculated with trig, but not a 90 degree angle, nor zero angle (it won't be parallel to the ground).
Your rifle barrel (bore) will be aiming up, at some angle to be calculated with trig, but not a 90 degree angle, nor zero angle (it won't be parallel to the ground).
You guys are making the concept much more complex than it really is.
Throw a ball underhand at something you are looking directly at. The trajectory of the ball when it leaves your hand has an upward angle, will cross your line of sight and then drops back to your line of sight as it reaches the target. A bullet with a properly sighted rifle does the same thing.
Got it?
Throw a ball underhand at something you are looking directly at. The trajectory of the ball when it leaves your hand has an upward angle, will cross your line of sight and then drops back to your line of sight as it reaches the target. A bullet with a properly sighted rifle does the same thing.
Got it?
That is my point, we talk about different procedures and mish mash an answer. Boresight is an alignment of two instruments while zero is the elimination of the all the effects on a bullet's trajectory to the best of one's ability.
Lets say you have a rifle that the bore is parallel with the sights. What's the problem with this idea? No more bullets "dropping in", rising, etc. No more sight in here and its the same again here. Well the problem is that your rear sight leaf would have to be about a foot long. So to make the rear sight shorter we have the bore angle different from the sight angle.
Wow, there is a lot of talk about this back and forth, but it's really easy:
The sights are on top of the rifle, right?. We'll ignore Special Relativity, so the line of sight, made up of light, will be straight. It's called "the line of sight" because it's the line through the sights.
If you ever want the bullet to cross that line of sight, and the sights to be "zeroed", then the bullet must be leave the bore (below the sights, remember) angled upward relative to the line of sight to cross the line of sight; therefore, the bore line and sight line are not parallel, if the rifle is zeroed. If they are parallel, you'll never get a "zero".
The point where the bullet crosses the line of sight is called the "Near Zero".
The bullet is travelling upward at this time, but gravity is at work, and will pull it back down in an arc. Think of a tossed baseball or football (is it too soon to mention football?), or of how the water hose arcs as you water your flowers.
The top of this arc is called the "Maximum Ordinate".
At some point the bullet will again cross the line of sight; this point is called the "Far Zero". So, in actuality, rifles typically have two distances at which they are zeroed.
For most scoped rifles, or rifles with tall sights (AR15), a near zero of around 25 meters (first time through the line of sight) will give a far zero of around 300 meters (second time through the line of sight). If I remember correctly, the actual near zero for a 20" AR15 A2 should be at 32 meters to get a 300 meter far zero.
If you have A2 sights, and want to zero your AR15 at 25 meters, use the "Z" setting (you know, "Z", like in "zero") on the rear sight, and adjust the elevation on the FRONT sight to zero. Then the built in Bullet Drop Compensator in the rear sight should be set pretty close. Use the "3" for 300 meters, "4" for 400, etc.
If you have a Garand, or M1A, the sights are much shorter. Therefore, the bullet's launch angle is shallower. This means the distance between the near zero and far zero is shorter, because the arc is shallower. If I recall, an M1 Garand with a near zero of 25 meters has a far zero of about 200 meters.
It's really simple. If the bullet crosses the line of sight, i.e., the rifle is zeroed, the bore line and sight line aren't parallel. If it is zeroed at some close distance, it will also be zeroed again further out.
Save all the trigonometry for discussing minute of angle and come ups.
We teach all of this on the 2nd day of an Appleseed training event. Sign up for one if you want to learn more!
The sights are on top of the rifle, right?. We'll ignore Special Relativity, so the line of sight, made up of light, will be straight. It's called "the line of sight" because it's the line through the sights.
If you ever want the bullet to cross that line of sight, and the sights to be "zeroed", then the bullet must be leave the bore (below the sights, remember) angled upward relative to the line of sight to cross the line of sight; therefore, the bore line and sight line are not parallel, if the rifle is zeroed. If they are parallel, you'll never get a "zero".
The point where the bullet crosses the line of sight is called the "Near Zero".
The bullet is travelling upward at this time, but gravity is at work, and will pull it back down in an arc. Think of a tossed baseball or football (is it too soon to mention football?), or of how the water hose arcs as you water your flowers.
The top of this arc is called the "Maximum Ordinate".
At some point the bullet will again cross the line of sight; this point is called the "Far Zero". So, in actuality, rifles typically have two distances at which they are zeroed.
For most scoped rifles, or rifles with tall sights (AR15), a near zero of around 25 meters (first time through the line of sight) will give a far zero of around 300 meters (second time through the line of sight). If I remember correctly, the actual near zero for a 20" AR15 A2 should be at 32 meters to get a 300 meter far zero.
If you have A2 sights, and want to zero your AR15 at 25 meters, use the "Z" setting (you know, "Z", like in "zero") on the rear sight, and adjust the elevation on the FRONT sight to zero. Then the built in Bullet Drop Compensator in the rear sight should be set pretty close. Use the "3" for 300 meters, "4" for 400, etc.
If you have a Garand, or M1A, the sights are much shorter. Therefore, the bullet's launch angle is shallower. This means the distance between the near zero and far zero is shorter, because the arc is shallower. If I recall, an M1 Garand with a near zero of 25 meters has a far zero of about 200 meters.
It's really simple. If the bullet crosses the line of sight, i.e., the rifle is zeroed, the bore line and sight line aren't parallel. If it is zeroed at some close distance, it will also be zeroed again further out.
Save all the trigonometry for discussing minute of angle and come ups.
We teach all of this on the 2nd day of an Appleseed training event. Sign up for one if you want to learn more!
The concept is not hard to understand, the problem lies in mixing two procedures boresight and zero into one. The picture below represents boresighting. The blue line from the scope to the target shows the displacement or offset from the line of sight. If you took out the bolt of the rifle shown you would see the target. along the green line is the height of the center of the scope above the center of the bore. No zero no ballistics just alignment. The lines are parallel.
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What if it's perpendicular?
Hey GAgun, here is a picture of what I am talking about
