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From Bryce Shooting - Point Blank Range |
| You
might have heard about sighting in my rifle using the “Point Blank
Range” method, but do you understand what it is? Any bullet starts to drop to the earth as soon as it’s free from the barrel of the gun. The line of sight is optical and unaffected by gravity and is straight from the shooter’s eye to the target. To compensate, the rifle’s bore is tilted at an angle to the line of sight. Because the bore of the firearm is below the sights, the bullet’s flight path will start out below the line of sight. It will cross through the line of sight, reach the peak of its arch (in relation to the line of sight) at some point and begin to drop again. Where the bullet’s path again crosses the line of sight is considered the “zeroed” range as the bullet will impact a target set at that range where the sights are line up on that target. The point blank range style of zeroing a rifle is to adjust the sights so that the bullet will not rise above or fall below a certain distance from the line of sight over a given range. For example, for a six inch zone the bullet will never rise more than three inches above the line of sight during its trajectory arc. At some point the bullet will drop below the line of sight and continue to drop. Where it drops below the line of sight by three inches is considered the maximum point blank range. It helps to envision this as shooting through a pipe, in this case a six inch pipe. The line of sight is exactly down the center of the pipe. The sights are adjusted so that the bullet’s path will never rise higher than the top of the pipe or fall below the bottom edge of the pipe until it reaches the maximum point blank range. The actual maximum point blank range is determined by the velocity and ballistic coefficient of the bullet. For example, a blunt nose .45-70 and a pointed .300 Winchester magnum will have much different MPBR distances when using the same target zone diameter. The theory behind this is that with a target zone of six inches (or whatever number you select) you can hold dead center on the animal and expect to hit the kill zone at any range out to the maximum point blank range. Of course, if you use this method you should allow some compensation for the variables such as shooter error, rifle accuracy, differences in animal size, wind, miscalculations in range, etc. If you are shooting at a deer with a ten inch kill zone it would be best to adjust the rifle for a six inch (never more than three inches above or three inches below the line of sight) point blank range. You can find information on point blank range for various cartridge and bullet options in many ammo catalogs or reloading manuals. All the popular ballistic computer programs can figure the exact point blank range for your rifle and load. Regardless of the method of sighting you choose, do it well, be fussy about getting it right and memorize the rifle’s trajectory until it is second nature to you when you shoot. |
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