eldeguello

The term "maximum point blank range" (PBR) is the distance at which a bullet will strikeat the bottom edge of the vital zone of the game you are hunting, when the rifle is zeroed so that it's maximum rise above the line of sight will not be higher than the TOP EDGE of that vital zone, IF you are aiming in the middle of the vital zone.

Let us use a big mule deer, for example. It may have a vital zone of, say, 6". You can zero your rifle so that the bullet will rise no more than 3" above the line of sight (LOS) from the muzzle out to where the bullet crosses the LOS againon the descending arc of its' trajectory. Beyond that point, the trajectory will continue downward in relation to the LOS, and at some point will be -3" from the LOS. That range is you MAX point-blank range, assuming you aim in the center of the 6" vital zone.

Now, let us say your quarry is elk, and you decide that the vital zone for a typical elk is 12", rather than 6". You canrezero your rifle so that the bullet willrisea maximum height of 6" above the LOS and still hit the vital zone with a center hold. It willalso still strike the vital zone after dropping as much a 6" below the LOS, again with a center hold.

The range at which it strikes-6" is now your new point-blank range for elk shooting. Note that the max PBR for shooting elk is a lot longer than the PBR for a big mule deer. If you are going aftersmaller animals or varmints with the same rifle, your PBR's are going to be a lot shorter.

So, as you can see, the PBR of a rifle depends on two things:

A. The flatness of its' trajectory
B. The size of the vital zone of the game you're pursuing

If you have a scope mounted say 3" above the center of the bore of a rifle, the bullet must travel downrange further before itcrosses the line of sight of that scope on the ascending portion of its' trajectory than it would if you had the scope mounted, say 1", above the line of the bore. This higher mounting plane makes itseem as if the trajectory of the bullet is flatter than it would appear to be if the line of sight and line of bore were closer together. The angle of departure of the bullet from the bore in relation to the earth is steeper. The bullet thus will be somewhat farther downrange before it falls enough to cross the LOS the second time as itdescends on the trajectory arc. This makes it look like the gun is shooting flatter, but the trajectory arc is actually unchanged.

Does this make sense??