Originally Posted By: IdahoelkaddictOriginally Posted By: BroncoGlennThere are two points that the bullet passes the line of sight. Once on the way up to the peak of its arc, the second on the way back down. The first point where it crosses the line of sight is referred to as the close range zero.
The catch is that every bullet flies a little different and different barrel lengths will produce different velocities. Different velocities will produce a different trajectory (arc) moving your close range zero point forward or backward relative to your distant zero range. After you have the velocity of the bullet and the ballistic coefficient for the bullet, you will also need the height of the sight above the bore to accurately compute your trajectory to get a close range zero.
Long story short: If you have 200 yards in which to shoot, zero at the 200 yards. You can use a close range zero to get on paper at longer distances, or to make sure you windage is dialed in. But otherwise, there is no replacement for shooting at distance you want to zero at.
You also have to recognize things like pronounced parallax occur with scopes at very close ranges unless you have an adjustable objective. Basically, with parallax it causes the reticle to move around on the target. You can see this when aiming by moving your eye up and down and side to side. If the gun is bagged or otherwise not moving, you will still see the reticle move around on the target. This can easily throw a round an inch off. An inch off at a close zero can put you way off at your distant zero.
For irons, however, the close zero can work well as it is easier to see the target (especially with older eyes), and the parallax is a non-issue. But you still want to check it at range.
I agree with this in that you should always zero at the distance you want to be sighted in at. You will find that different ammo based on different BC of the bullet and different velocity will not shoot the same comparatively at different distances and won't "match up" at a short and long range.
It is incorrect, however, that a bullet "passes the line of sight twice." The "peak of its arc" is the muzzle. As soon as that bullet leaves the barrel gravity is pushing it downward. It never gains elevation. Your sight device, be it iron or scope, must align with the bullets path and that is what you are trying to coordinate to the trajectory of the bullet. Technically you are angling your rifle upward to create an "arc" because your sigts are above the plane of the bullet's travel.
Semantics I suppose, and BroncoGlenn is otherwise spot on. I'm probably picking the fly crap out of the pepper, but I heard another guy at the range the other day trying to explain this and was telling some new shooters how the bullet gains elevation and then drops after time. It was confusing and I thought I would just take an opportunity to clarify.
Your clarification is confusing. The bullet does gain elevation due to the angle of the rifle, it does cross the line of sight twice, and the apex isn't at the muzzle at least not usually.