HUNTING WITH AIRGUNS
by Jim House
Chapter 7: Airgun projectiles.
In recent years, enormous strides have been made in producing air rifles that have greater power and accuracy. However, these efforts would be of little effect if it were not for the fact that developments in projectiles have also kept pace. There is an airgun projectile for almost any conceivable use.
Historically, round projectiles have been used in both firearms and airguns. Lead BBs were very popular and regularly used when I was a lad. However, there were some problems associated with the use of lead BBs. In addition to the toxicity issue, lead is soft, and a deformed BB would often jam in the feeding mechanism. Steel BB shot have been the preferred type for many years. A BB is an inefficient projectile in flight, and a smooth bore is not conducive to high accuracy. BB guns are not suitable for humane hunting activities and they should never be used in that way.
If you examine most types of lead pellets that were manufactured half a century ago, they generally appear to be thin lead cups with flat noses. The notable exception are the .20 caliber pellets that were produced for Sheridan air rifles. They were solid and cylindrical in shape, and they had a thin flange around the base to provide an air-tight seal in the bore. In addition, the noses were rounded in shape more like a bullet. The Sheridan pellets were known for their outstanding ballistic efficiency and penetration. As a result, Sheridan air rifles were the choice of many hunters who wanted to engage in their sport using an air rifle. Although the pellet design has been changed somewhat over the years, the Sheridan is still the air rifle chosen by many hunters.
Today, almost all pellets have a shape that is characterized by three sections. The front section (also referred to as the nose) may be flat, rounded, or pointed, but is comparatively solid in construction. When compared to firearms, air rifles operate at low pressure. In order to have the pellet seal the bore against the compressed air pushing on the base, pellets are hollow to some degree. The base section (also referred to as the skirt) is typically thin so it can expand to fill the bore. In some cases, the thin section continues forward so the pellets have large internal cavities and are essentially hollow. Between the head and the skirt is the midsection of the pellet, and it is almost always of smaller diameter than the other sections. The result is that only the head and skirt make contact with the barrel in order to reduce friction between the pellet and the barrel. Although most pellets have these general design features, there is still an enormous variety in pellet types.
Because they are made as essentially hollow shells with blunt noses, lead pellets of older designs have a lot of air resistance and lose velocity rapidly. This is true of modern pellets of the wadcutter type, and they typically have ballistic coefficients as low as 0.010. On the other hand, a well-shaped pellet with sturdy construction may have a ballistic coefficient as high as approximately 0.030. In comparison, a pointed projectile like those used in center fire rifles may have a ballistic coefficient in the range 0.300-0.500. Even the most aerodynamic airgun projectiles are very inefficient compared to bullets fired from firearms. Let us suppose you are going to hunt with a .25 caliber air rifle that has a muzzle velocity of 700 ft/sec. Figure 4 shows how the loss of velocity is related to the ballistic coefficient for two pellets having that muzzle velocity. Even at a distance of 30 yards, there will be a difference of approximately 100 ft/sec in the remaining velocity. This corresponds to a substantial difference in energy.
Figure 4. A comparison of velocities for pellets having ballistic coefficients of 0.010 and 0.020 over a range of 50 yards.
Pellets are produced in many different shapes. The wadcutter design has been popular for many years, and it is still the preferred style for competition in which paper targets are employed. These pellets cut a clean hole in the target which aids in scoring. They are also suitable for taking small species at short range because the flat nose hits hard. However, penetration is much less than that provided by pointed or round nose pellets so wadcutter pellets should be used only on species that do not require much penetration.
A pellet with a rounded or pointed nose passes through air with less resistance than one with a flat nose. This results in better velocity retention and much better penetration. As a result, pellets having these designs have become very popular with hunters. However, even some very wicked looking pellets with sharp pointed noses do not have high ballistic coefficients because they have such large internal cavities. The outer profile is important, but so is the internal construction. Pellets having solid interiors penetrate better whereas the more hollow pellets tend to flatten or rivet.
In recent years, the hollow point pellet has become popular. The idea is that when the pellet strikes the target, it will expand to create a larger wound channel. This is generally the case if the velocity is sufficiently high, but some hollow pointed pellets do not expand reliably at low velocity.