Difference between revisions of "Rifle Trajectory Table"

Revision as of 17:36, 11 December 2010

By Chuck Hawks

In order to hit a distant target a rifle must be correctly sighted-in, and to accomplish that the shooter must have some working knowledge of the bullet's trajectory. Sighting-in a hunting rifle to hit a certain number of inches high at 100 yards (or 100 meters) maximizes the point blank range of the rifle and cartridge and is superior to zeroing at a fixed distance like 200 yards. This system maximizes the distance in which no "hold over" is necessary. Of course, the actual distance the bullet should hit above the point of aim at 100 yards (or 100 meters, which is about 108 yards) varies with the individual caliber and load.

The table below is designed to serve as a starting point from which a shooter can work. Used as such it can save a lot of trial and error experimentation. Of course, no trajectory table can possibly cover all loads for all calibers in all rifles. So after sighting-in, always check your individual rifle at various ranges to see how close its trajectory comes to the published data. (It may well vary.) This trajectory table can also serve as a comparative tool, allowing the reader to compare the trajectories of different cartridges or loads.

The trajectories in the table below were calculated for a maximum bullet rise of 1.5 inches above the line of sight for all small game and varmint loads, and three inches above the line of sight for all big game loads. In ballistics catalogs the point of maximum bullet rise is often called the mid-range trajectory, or sometimes the maximum ordinate. In the table below I used the term "mid-range trajectory," abbreviated "MRT."

A maximum bullet rise of 1.5 inches is appropriate for shooting small animals, as they present a small target, particularly if head shots are necessary. Allowing a greater mid-range trajectory might result in shooting over an animal at an intermediate distance.

A maximum rise of 3 inches is appropriate for hunting the smaller species of big game, creatures from perhaps 75 pounds to 150 pounds on the hoof, which typically have a kill zone of about 8 inches from top to bottom. More mid-range rise can be accepted when hunting larger animals (a 4 inch MRT might be appropriate when hunting mule deer, for example), but if a mixed bag hunt for larger and smaller species is envisioned, then the 3 inch rise used for this table is probably safer. A 3 inch MRT also allows for a little bit of human error, which is probably a good thing when shooting in the field.

The Maximum Point Blank Range (MPBR), which is shown in the last column of the table below, is the distance at which the bullet falls 3 inches below the line of sight. Thus between the muzzle and the distance given as the MPBR, the bullet never strays more than 3 inches above or below the line of sight (1.5 inches for varmint loads).

Most of the loads below are similar to popular factory loads for the selected cartridges. All trajectories were calculated for a rifle with a low mounted telescopic sight of moderate size whose line of sight is 1.5 inches above the bore axis of the barrel. If your scope is not 1.5 inches over the bore, and most scopes with oversize objectives require higher mounts, your trajectory will vary from those given below. All trajectory figures are rounded off to one decimal place. While environmental factors such as altitude and ambient air temperature affect trajectory, their effect is relatively minor. For the record, this table was calculated for an air temperature of 60 degrees F and an altitude of 1000 feet. The following data was taken from various sources including reloading manuals and the online Ballistics Calculator provided by BigGameInfo.

To save space, the following abbreviations are used in the table below: Wb = Weight of bullet (in grains); MV = Muzzle Velocity (in feet per second); BC = Ballistic Coefficient; MRT = Mid-Range Trajectory; yards = yds.; inches = "; MPBR = Maximum Point Blank Range; BT = Ballistic Tip; FP = Flat Point, HP = Hollow Point; RN = Round Nose; Sp = Spitzer; SP = Spire Point; SSp = Semi-Spitzer.