Velocity, energy and accuracy

Air rifles, like any firearm, provide a degree of effectiveness that largely depends upon their velocity, energy and accuracy. But how they go about achieving each can differ greatly from traditional firearms.

Velocity is how fast a projectile travels when exiting the barrel and generally is referred to in terms of feet traveled per second. Some of the best air rifles are capable of sending projectiles at speeds exceeding 1,200 feet per second, which can prove make them very good small game hunting implements. With an air rifle or air gun, the velocity is determined by the amount of compressed air, the barrel and the projectile. The more compressed air that is available, the greater the potential velocity. But, some of that compression can be lost if there is a poor seal between the barrel and the projectile. Compression also can be lost to some degree when using shorter barrels.

In general, the longer the barrel, the more compression is contained to launch the projectile and the greater the velocity and muzzle energy. But that velocity tails off rapidly. By the time a pellet has traveled 100 yards, it has lost at least half of its velocity. The pellet also will lose its accuracy if shot at a muzzle velocity exceeding 1,100 feet per second, which is the speed of sound.

When a pellet breaks the sound barrier, it creates a shock wave capable of destabilizing the projectile. When it drops back below 1,100 feet per second, the pellet can tumble and lose its integrity. In many instances, an air rifle that shoots pellets at less than 1,100 feet per second can be very accurate, although a high degree of accuracy also is available from air rifles capable of launching pellets well beyond the speed of sound.

Energy is another function of velocity and can increase the velocity when there is more energy available to propel a pellet. In firearms, energy generally is referred to as muzzle energy and is measured in foot-pounds of energy. With air rifles, the muzzle energy generally is low and can determine whether or not an air rifle is legal in some nations that have limits on how much muzzle energy an air rifle can produce to remain legal. Exceeding the muzzle energy limit can make the rifles more lethal and, therefore, illegal.

Muzzle energy is determined by a formula measuring the velocity in feet per second and utilizing the weight of the projectile. If a projectile is eight grains and it travels 800 feet per second, the formula begins by multiplying the weight in grains, eight, by the square of the muzzle velocity. The total then is divided by a constant, which is 450,240, and results in a muzzle energy of 11.37 foot-pounds of energy. For the sake of simplicity, whenever the muzzle velocity is 671 feet per second, the muzzle energy always is equal to the weight of the projectile. So an eight-grain projectile traveling at 671 feet per second when existing the muzzle would have a muzzle energy of eight foot-pounds.

Accuracy in an air rifle essentially is the function of several key components. The first is the barrel itself. Many high-end air rifles in fact are rifles with some measure of rifling inside the barrel that will put a spin on the projectile. While the spin is nothing like that induced by firearms rifles, which rely greatly on bullet spin to create accuracy, the spin created by rifled barrels on air rifles are much less effective but still can enhance accuracy to some degree. As with a firearm, the longer the barrel, generally, the better the accuracy due to having more spin and higher rates of compression mean the projectile will travel further with less drop.

Using accurate iron sights on longer barrels is another component of accuracy with an air rifle. The greater the distance between the front and rear sights, the less likely the shooter is to have the target off-angled. Longer barrels make it easier to find the sight picture and place the projectile within it.

The projectile itself is another critical component of accuracy. A pellet can be configured in different shapes, weights and compounds. In general, an effective pellet has a weighted head, pinched waist, which is referred to as a “wasp waist,” and is skirted to maintain flight integrity. The skirted tail captures the compressed air as the projectile is in the barrel. So long at the skirt maintains a relatively tight seal with the barrel, it will benefit from the full power of the compresses air. But if the skirt does not create a proper seal, some of the compressed air will escape and decrease energy, velocity and accuracy.

The design of the pellet makes a great deal of difference in its effectiveness and accuracy. With the heavy nose and skirted tail, it acts like a badminton shuttlecock with the flight stabilized by the forward weight and the tail providing drag to maintain the flight path. Although rifled barrels will put some spin on the projectile, the spin itself is not enough to maintain accuracy. Instead, the hollow skirted tail keeps the pellet stable while in flight while the spin helps to improve its range and accuracy.

The weight of an air rifle or any firearm also can make a difference in the degree of accuracy. If a shooter is overmatched by the weight, the accuracy will suffer. The ability to properly hold and sight an air rifle has a tremendous impact on its accuracy. So long as the sights are aligned, the air rifle is in good shape and the barrel is of sufficient length, a high degree of accuracy is obtainable. That high degree of accuracy is demonstrated by the hunting effectiveness of air rifles when going after small game, such as rabbits and squirrels, and when Olympic competitors use them in shooting contests. Within 100 yards, air rifles can be incredibly accurate.

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