5.5 Point Blank Range
Point blank range is a concept which is extremely useful to hunters, and it is well understood by most of them. This idea is also important for some types of target shooting, as, for example, silhouette shooting. The point blank range of any gun is the distance out to which a hunter can hold right on this game and be assured of a hit within a vital zone of the animal. In other words, the hunter doesn’t have to hold high or low to correct for the bullet trajectory.
In a sense, point blank range is a measure of how flat a gun will shoot. It is clear, though, that point blank range depends on the size of the game animal, as well as on the cartridge and load used in the gun, since, for example, the vital zone of a varmint is considerably smaller than the vital zone of a deer-sized animal. What we wish to point out in this section is that there is a practical way tomaximize the point blank range of any cartridge, and this can be done just by selecting the right zero range for the gun, which in turn depends on the size of game animals for a particular hunt.
Surprisingly, maximum point blank range usually turns out to be considerably larger than you might expect. For example, suppose you have a .30-30 Winchester with iron sights and you load Sierra’s 150 grain flat nose bullet to 2200 fps muzzle velocity. In today’s magnum world, you can’t expect much from a .30-30 load. Most gun writers won’t even mention a .30-30 for deer where ranges might exceed 150 yards. However, the maximum point blank range of your load is 220 yards for deer-sized game! You have to zero your rifle in at 180 yards in order to get the 220 yard maximum point blank range. Under these conditions, you will find that your bullet trajectory never rises more than 5 inches above your line of sight (at ranges shorter than the zero range), nor will it fall more than 5 inches below your line of sight until ranges exceed 220 yards. Your point blank range is maximized for animals with a vital zone 10 inches in height.
Of course, we must hasten to add that the maximum point blank range of a .300 Winchester Magnum firing Sierra’s 150 grain spitzer flat base bullet at 3200 fps is 370 yards for deer-sized game. The big magnums have an appreciable edge over lower velocity cartridges in the point blank range department, just as we expect. The central point of these examples, though, is that maximizing the point blank range for your rifle and for the game you are going after can really help you bag it, because it helps relieve uncertainties about where to hold when you don’t know how far away the animal is. For this reason, Sierra has included maximum point blank range (and the correct zero range to reach the maximum) in the Ballistics Tables of this Manual. If you glance ahead to the Ballistics Tables, you will find these values listed for every bullet and every muzzle velocity level.
Figure 5.5-1 illustrates the vital zone for a deer. A hit within this zone is likely to kill the animal instantaneously, or disable it so that it can be quickly dispatched with a second shot. The point blank range concept calls for the hunter to aim at the center of this zone. Then, as long as the animal is not farther away than the maximum point blank range, a well-aimed bullet will strike within the vital zone. Sierra has chosen to use a vertical vital zone dimension of 10 inches for deer and larger game. This choice might be too small for larger North American game, but it is reasonable for the majority of game hunted on this continent. For varmints and small game, we have chosen 5 inches as the vertical dimension of the vital zone. This choice might be a little large for very small animals like ground squirrels, but it is reasonable for rabbits, woodchucks, and larger varmints. For rifle and handgun silhouettes, we have chosen 6 inches as the vertical dimension of the vital zone for the steel targets.
The vital zone dimension selected for each bullet is listed at the top of each page of the Ballistics Tables, and the selection for each bullet depends on its primary purpose. For example, the .22 caliber 40 grain Hornet bullet is used primarily for varmints and small game. The top line of the first page of the Ballistics Tables reminds us that the maximum point blank range occurs for a trajectory which rises 2.5 inches above the line of sight and then falls 2.5 inches below it, for a total vital zone dimension of 5 inches.
This trajectory relationship is shown pictorially in Figure 5.5-2 . Notice that the line of sight goes down the center of the vital region. When the point blank range is maximized, the bullet trajectory rises above the line of sight and just touches the top boundary of the vital zone. Then, the maximum point blank range is the point where the bullet trajectory crosses the lower boundary of the vital zone. This has to be the condition which maximizes point blank range, because if the trajectory does not rise far enough to touch the upper boundary, it will cross the lower boundary at a range shorter than the one shown in the figure. The zero range shown in the figure is the value that makes the trajectory just touch the upper boundary, so it is the right choice to maximize the point blank range.
Figure 5.5-2 is the trajectory picture for which the point blank range values in the Ballistics Tables are given. For each bullet and for each muzzle velocity level in the Tables list both the maximum point blank range and the zero range which must be used to obtain it.