THE BALLISTIC COEFFICIENT

Written by: Der Luftmeister

If I am shooting my airgun at targets placed no farther than 10 meters away, I worry only about the accuracy of the pellet I am using. However, when I am roving with an airgun, I may encounter targets of opportunity at ranges from a few feet to as far as 50 yards or more. In that case, my concern is that the pellet retain its velocity to the greatest extent possible. The result is a trajectory that has the least curvature which in turn makes it easier to hit nearer the point of aim. It also means that the retained energy is as high as possible which is important if the target is some animal that is to dispatched cleanly.

When it comes to being able to move through air with minimal velocity loss, not all pellets are created equal. The ballistic coefficient is simply a number (in almost all cases between 0 and 1) that gives an index of how well a projectile in flight resists the retardation by air. It is a sort of batting average of the projectile against the atmosphere. In baseball, the higher the batting average the greater the likelihood the batter will get a hit. In ballistics, the higher the ballistic coefficient, the greater the fraction of the velocity retained as the pellet passes through air.

Pointed bullets used in center fire rifles have ballistic coefficients as high as 0.400 or 0.500 in many cases. If two bullets of identical weight have ballistic coefficients of 0.400 and 0.440, the difference is 0.040 which is only 10 percent. The difference in retained velocity will not much different for the two bullets if they are fired at the same muzzle velocity.

Although there are exceptions, the ballistic coefficients of airgun pellets are usually in the range of 0.010 to 0.030. That means that pellets lose their velocity rapidly. When comparing a wadcutter pellet having a ballistic coefficient of 0.010 with a pointed pellet that has a ballistic coefficient of 0.020, the difference is only 0.010, but that is a 100 percent advantage for the pointed pellet! Let us illustrate with a specific example.

Suppose your favorite .177 caliber Luftgewehr (air rifle) fires a 7.9 grain wadcutter pellet having a ballistic coefficient of 0.010 with a muzzle velocity of 800 ft/sec. Calculations show that the pellet will arrive at a target 40 yards from the muzzle traveling at 483 ft/sec. Now suppose a pointed pellet having a ballistic coefficient of 0.020 is fired with the same muzzle velocity. According to calculations, the pointed pellet will arrive reach a target at 40 yards with a retained velocity of 620 ft/sec. That is a 28.4% greater velocity for the pointed pellet.

When it comes to retained energy, the difference is even more dramatic because energy varies as the square of the velocity. In one case the remaining energy is 4.09 ft lbs while in the other it is 6.74 ft lbs (a 65% advantage for the pointed pellet). If your quarry is a critter, this difference could mean the difference between success and failure.

A higher ballistic coefficient not only means greater retained energy, but also a less curved trajectory. Suppose the rifle is sighted in at 30 yards. If we take the two examples of pellets and velocities described above, calculations show that the wadcutter will strike almost 1.5 inches low at 40 yards while the pointed pellet will have a point of impact that is almost exactly 1 inch low. The difference is not great, but if the lethal zone on your target is only about an inch in diameter, flatter trajectory is a great asset.

As a an approximation, the ballistic coefficients of flat pointed pellets such as Hobby and Meisterkugeln are around 0.010 to 0.012. The values for most domed pellets are around 0.015 to 0.020. For example, in .177 the Crosman Premiers are 0.023 and 0.027 for the light and heavy versions, respectively. These are among the highest values for .177 pellets. The .22 caliber Crosman Premier has a ballistic coefficient of approximately 0.028 and in .20 caliber the value is almost 0.040. Crosman pellets have very shallow base cavities and solid construction in the head area so their ballistic coefficients tend to be rather high. The .22 caliber 21.1 grain Beeman Kodiak has a ballistic coefficient of about 0.036 and is of solid construction. Some other domed pellets that are of a more hollow design have lower ballistic coefficients.

A pointed pellet does not always assure a high ballistic coefficient. For example, the Dynamit Nobel SuperPoint has a value of only about 0.012 because of the way it is constructed.

So you want to use the pellet with the highest ballistic coefficient to shoot at pigeons at 50 yards, right? Well, the most important consideration is accuracy. It does not do any good to have more remaining energy if the pellet does not strike where you want it to. But if two pellets give equal accuracy, I select the one with higher ballistic coefficient if I anticipate taking shots at relatively long ranges.

Stay pumped.

AIRGUNS ARE FOR MAKING MEMORIES

Written by: Der Luftmeister

Each of us is a product of the experiences and environments that have brought us to where we are. For the readers of this web site, those shaping influences may well have included contact with airguns. In my own case, I started with an old Daisy single shot BB gun more than three score years ago. Since I grew up in a rather remote area, that little BB gun was carried countless miles through fields and woods. My father had owned a multi-pump Benjamin in his younger days so I heard about the feats that it performed. The point is that airguns have always been a part of my culture. That is not to say that I have been an active air gunner all these years, but the seeds were always there.

Almost 20 years ago, I bought a Crosman 2200 multi-pump. That was also a result of some history because a cousin had a .22 Crosman when I was a young lad. It was an impressive piece so I had always wanted an equivalent airgun. While visiting with my father, he had a chance to examine and shoot my Crosman 2200 which resulted in his wanting one. The result was that Dad got a Crosman 2200 although by that time his sight was not very good and he didn’t shoot it much. After Dad passed on, several of his possessions were distributed between my brothers and me by lot, and one of my drawings gave me his Crosman 2200. Already having two or three others, the airgun had only sentimental value, but that was strong. In order to perpetuate the attachment for that particular airgun, I quickly passed it on to my son. Now he has Dad’s Crosman 2200.

This story is hardly unique. I have talked to numerous people who have told me stories about how they came to have a particular airgun. Properly cared for, airguns are durable and have long life. There is no reason why they can’t be passed on for generations.

As we travel, my wife and I make it a point to stop at antique malls and occasionally at pawn shops. It is from these sources that some of my cherished collectible airguns have been obtained. No doubt you have engaged in similar searches. When you find a piece you want to collect, have you ever wondered if it could talk what stories it could tell? Perhaps it was a gift to someone many years earlier. It may have been used for a time only to be passed on to someone else. Perhaps it was replaced by a better model so it fell in disuse. Perhaps when the original owner passed on, the airgun was no longer wanted by other family members. Whatever the reason, it became available to those of us who collect and use airguns. As we all know, need has nothing to do with it.

One sad aspect of this story is that when I was a young lad shooting airguns, my father did not own one and would have scarcely had time to spend using it. When he did have the time, I was long since gone and did not have the time. The result is that although we both had an interest in airguns, we shared no special times in which our common interest gave us memories. In spite of the many other wonderful aspects of using airguns, it is my opinion that the most valuable part of the activity is in sharing it with others. Take time to introduce others to our wonderful sport. It is through such mentoring that memories will be made, but more importantly, it is the only way to assure the survival of our sport.

You may be familiar with the song, “Puff the Magic Dragon” that was popular a generation ago. One line in the song tells that dragons are forever, but not so little boys (and girls). As the boy in the song grew older, he had no further need for Puff. Sadly, as many boys and girls grow older today, they have no use for airguns. It is time to stress the positive, wholesome, and recreational aspects of our sport.

Until next time, stay pumped up about air gunning.