3.5 Point Blank Range
Point blank range is a concept that is very important to hunters and silhouette target competitors. The point blank range of any gun is the range distance out to which a shooter can hold right on his game or target and be assured of a hit within the vital zone of the animal or target. In other words, the shooter does not have to hold high or low to correct for the bullet trajectory. This eases the problem that many hunters have of estimating the distance to a game animal. As long as the range to a game animal is not farther than the point blank range of the gun, the hunter can aim at the center of the vital zone on the animal and be assured of a hit. For silhouette competitors, the point blank range idea can reduce the number of sight adjustments necessary for the targets at longer ranges.
The vital zone of an animal is a zone within which a bullet will put the animal down, either killing it instantly or disabling it so that it can be quickly dispatched with another shot. For a silhouette target, the vital zone is an area on the steel animal profile within which a hit will tumble the target. Of course, the size of the vital zone depends on the size of the animal. Only the vertical dimension of the vital zone is important for calculation of the point blank range, because the bullet trajectory arcs upward and downward in a vertical plane. In the horizontal direction, the shooter must aim and place his bullet within the horizontal edges of the vital zone, but on a large animal the vital zone may be considerably wider than it is high.
For animals like white tail deer, the vertical dimension of the vital zone is about 10 inches, from a point on the shoulder of the animal down to the level of its heart. For the larger mule deer, the height of the vital zone might be 11 or 12 inches and about 14 inches for elk. For small varmints, such as prairie dogs, ground squirrels and ground hogs, a vital zone height of 5 inches is appropriate. For rifle silhouette targets, a vital zone height of 6 inches seems appropriate. These estimates, of course, can be changed based on the shooter’s judgment.
Figure 3.5-1 illustrates the concept of the point blank range. The vital zone region extends from the gun muzzle to the game animal or silhouette target. The shooter’s line of sight goes down the center of the vital zone region, indicating that the shooter aims at the center of the vital zone on the animal or silhouette. The figure shows the special situation in which the point blank range is maximized. The bullet trajectory rises above the line of sight until it just touches the upper edge of the vital zone. Then the trajectory falls through the zero range and on through the lower part of the vital zone region. The maximum point blank range is then the range distance at which the trajectory crosses the lower edge of the vital zone. If the animal or target is positioned anywhere within this point blank range, a well-aimed bullet will put it down.
Point blank range is maximized by choosing the correct zero range for the gun, that is, the zero range that causes the trajectory to rise just to the upper edge of the vital zone region. If a shorter zero range is chosen, the trajectory will not rise as far as the upper edge of the vital zone region, and the trajectory will then cross the lower edge of the vital zone region at a point blank range that is shorter than the maximum possible. It is clearly desirable to maximize the point blank range for game in all hunting situations, and there are advantages in the silhouette games as well.
Figure 3.5-1 Illustrating the Point Blank Range of a Gun
Infinity will calculate point blank range for either of two situations. The first is when the shooter has already zeroed in his or her gun for a specific zero range. This situation is the selection labeled “PBR – Given Zero” in the drop-down menu under “Operations” in the topmost Infinity toolbar. For this situation, Infinity first determines whether the specified zero range is less than or greater than the zero range that maximizes point blank range for the cartridge, load and environment parameters inputted by the shooter. If the zero range is less than that which maximizes the point blank range, a message on the monitor screen will inform the shooter, that this condition is true, and also tell the user what the reduced (submaximal) point blank range is. On the other hand, if the specified zero range is greater than that which maximizes point blank range, a message on the monitor screen will inform the user, that this condition is true, and then tell him the maximum point blank range for the vital zone height that was chosen and what zero range to use to obtain the maximum point blank range.
The second situation is the selection labeled “PBR – Maximum PBR” in the “Operations” dropdown menu. In this situation the user wants to know the maximum point blank range for his or her cartridge, load and shooting conditions, and what zero range to use to obtain that maximum range. In this case, Infinity will output those parameters on the monitor screen and also list a trajectory calculated for the maximum point blank range condition. This gives the shooter the necessary information to sight in the gun so that the maximum point blank range is obtained.
Before using Infinity for either of these point blank range calculation modes, recall that it is necessary to first calculate a reference trajectory for the cartridge, load and shooting conditions at the hunting location or the target range location. This is done using the “Trajectory” selection in the drop-down menu under the “Operations” selection in the topmostInfinity toolbar.
Maximum point blank ranges are surprisingly long for both rifles and handguns. Of course, the high-velocity, flat-shooting magnum calibers have a decided advantage over lower-velocity cartridges with bullets having lower ballistic coefficients. But, the maximum point blank ranges of even ballistically inferior bullets are quite long. To cite a few examples, against deer-size animals (vital zone height 10 inches), calculated for an altitude of 1000 feet and standard atmospheric conditions:
|Cartridge Bullet||Muz. Vel.||Max. PBR||Zero Range|
|300 Win. Mag. 180 gr SBT GameKing||2800 fps||345 yds||292 yds|
|308 Win. 165 gr SBT GameKing||2650||319||271|
|30-30 Win. 150 gr FN Pro-Hunter||2200||247||211|
|45-70 Gov’t 300 gr HP/FN Pro-Hntr||1550||179||152|
|44 Rem. Mag. 240 gr JHC Sports Mstr.||1300||151||127|
|357 Magnum 170 gr JHC Sports Mstr.||1050||131||110|
Examples of maximum point blank ranges against small varmint-size animals (vital zone height 5 inches) calculated for an altitude of 1000 feet and standard atmospheric conditions are the following:
|Cartridge Bullet||Muz. Vel.||Max. PBR||Zero Range|
|243 Win. 55 gr. BlitzKing||3800 fps||311 yds||269 yds|
|22-250 Rem. 55 gr. Blitz||3600||301||259|
|223 Rem. 55 gr. Blitz||3000||257||221|
|22 Hornet 45 gr. Hornet||2650||208||180|
These examples clearly show that the maximum point blank ranges of cartridges are surprisingly long for animals with relatively small vital zone heights. This targeting technique has a great deal of utility.