Air-Gun Ballistics Conspectus

We are going to add a page showing the relation between: Speed, Reservoir Pressure, and Ft lbs. [or energy of a projectile measured at the moment it exits the muzzle] for each one of the DrillDog Big Bore Pellets, but first we would like to mention a few notes taken from the Crosman website (crosman.com/get-hunting/airgun-ballistics) which can be applied in general terms to all Air Guns’ Ballistics, although pcp--pre charged pneumatic--airguns have a slightly better trajectory due to the cylinder’s highly compressed air; nevertheless, it gives you an idea of the importance in shot placement to obtain accuracy, and their remarkable differences with firearms.

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AIR GUN BALLISTICS

As soon as a pellet or any other projectile leaves the muzzle, the force of gravity starts to work on it pulling it downward. This results in a projectile following a curved path known as the trajectory. Sighting involves looking in a straight line. Therefore, there is some discrepancy between the line of sight and the path of the projectile. The sights are placed on top of the barrel so the bore is actually below the line of sight. If a scope sight is utilized, the bore may be as much as an inch and a half below the line of sight.

The pellet rises (because it is fired slightly upward) to meet the line of sight. The distance at which the projectile meets the line of sight is the distance at which the rifle is “sighted in.” In most cases, the trajectory crosses the line of sight as the pellet rises and then crosses it again as the pellet continues on its downward path. The height of the bullet path above the line of sight at the midpoint of the sight in distance is referred to as the midrange trajectory. Thus, the rifle is actually sighted in at two distances, the longer of which is generally considered to be the distance for which the rifle is sighted in. This situation is illustrated in Figure 2 which shows typical trajectories for identical pellets fired at 600 ft/sec and 800 ft/sec.



In both cases, the rifles are sighted in at a range of 30 yards. Note that the path of the pellet crosses the line of sight in two places one of which is 30 yards. But the pellet also crosses the line of sight at a shorter distance that depends on the velocity of the projectile. Note also that the heights of the trajectories above the line of sight at a range of 15 or 20 yards differ with the slower moving pellet having to rise higher in order to cross the line of sight at a distance of 30 yards, the sight in range. We say that the faster moving pellet shoots “flatter” meaning that its path has less curvature than one traveling slower. Note also that when the rifle is sighted in at a distance of 30 yards, the path of the pellet at 50 yards is about 6.6 inches low when the muzzle velocity is 600 ft/sec but only about 3.2 inches below the line of sight if the muzzle velocity is 800 ft/sec. It is readily apparent that a high muzzle velocity makes it easier to hit small objects at longer ranges.

As has been mentioned, the higher the ballistic coefficient the less rapidly the pellet loses velocity. That principle is demonstrated graphically by considering two pellets that have ballistic coefficients of 0.010 and 0.020 when both leave the muzzle at 900 ft/sec. Figure 3 shows the remaining velocity of such pellets over a range of 50 yds.



The point of understanding ballistics as applied to airguns is that the hunter should know the limitations imposed by power, accuracy, and skill. Do not attempt to stretch the range of an airgun beyond what is certain.

September 2017.