5.0  Exterior Ballistics Topics

5.0  Exterior Ballistics Topics

 This section addresses several topics in exterior ballistics which are of keen interest to both hunters and target shooters. 

Section 5.1 describes effects of altitude above sea level and atmospheric conditions on bullet trajectories. Ballistics tables in this Manual and in other references are calculated for sea level and so-called “standard” atmospheric conditions. Section 5.1 shows how we can calculate an “equivalent” ballistic coefficient for a bullet fired at an altitude above sea level and in other weather conditions, and use the sea level standard ballistics tables with this equivalent ballistic coefficient to find the bullet trajectory.

  Section 5.2 then describes trajectory variations for some specific classes of Sierra bullets fired at different altitudes, and also describes what happens to bullet trajectories when they are fired uphill or downhill. The question of whether a gun shoots high or low when it is fired uphill or downhill is answered. (You may be surprised to learn that every gun shoots high when it is fired either uphill or downhill!)

  Section 5.3 describes effects of winds on bullet trajectories. Effects of headwinds, tailwinds, crosswinds, and even vertical winds are treated in that section.

  Section 5.4 discusses the subject of zeroing in, describing relationships between the bullet trajectory, the sight height, and the line of sight. The section shows how to zero your rifle for a range of, say, 250 yards when you must use a shorter target range, say 100 yards. The section answers some other questions frequently asked in letters and telephone calls from shooters.

  Section 5.5 describes the concept of point blank range, which is of interest mainly to hunters and silhouette shooters. Point blank range is the maximum range for any gun and cartridge/load combination within which the shooter does not need to hold high or low in order to place his bullet in a vital zone of the target. This optimum range depends on the trajectory of the bullet and on the size of the vital zone. Section 5.5 shows that the point blank range of any load for a game animal or silhouette can be maximized simply by choosing the right zero range for the gun.

 Finally, Section 5.6 describes a relationship between the muzzle velocity of a gun and the temperature of a cartridge and its components at the instant of firing. The temperature of the primer and powder has a very strong effect on muzzle velocity for most rifle cartridges, and a smaller but still important effect in most handgun cartridges. This section describes some measurements made to illustrate these effects.