Ballistics And Statistics

Statistics: the branch of mathematics that deals with the collection, organization and interpolation of numerical data. Statistics is especially useful in drawing conclusions about a set of data from a sample of the data. (See mean, median, mode, normal distribution curve, sample, standard deviation and statistical significance.) Typical problem: estimating true value of parameters from a sample of data.

 

- Dave Scovill

The paragraph above is a brief Internet summary from diction ary.com, but is fairly close to the orientation sheet passed around the classroom on the first day of a statistics course during my junior year at the University of Oregon. It was pretty droll stuff, but a required course for my major in architectural design and engineering. Oddly enough, it became one of the most interesting aspects of my writing 40 years later.

It all came home when I purchased a Custom Chronograph with printed screens back in the late 1970s. The system was fairly straight forward: Mount a screen in each set of two clips mounted at either end of a 2-foot piece of plywood. The clips were wired to a unit that read the velocity of the bullet, BB or arrow that was fired through both screens, starting and stopping an electric circuit that was converted to velocity in feet per second. Screens were replaced after each shot, and were sold in packs of 100 to 1,000.

Sometime after purchasing the Custom Chronograph, Dr. Ken Oehler came out with the new Oehler Model 33 Chronograph that not only determined velocity but also calculated Standard Deviation (SD) for each string of shots. Right off, writers around the industry began to assert that SD could be used to predict accuracy. That is, lower SD numbers implied better accuracy potential than higher SD numbers, which also implied a great deal of gullibility on behalf of anyone who might believe that – simply because there was no standard method to apply SD by the number of shots in each set or group, or the number of sets required to validate SD.

There were also other factors to consider other than velocity, such as variations in bullet weight/ diameter, charge weight and case weight/volume, that might collectively, or individually, affect accuracy, which is/was not to ignore the simple fact that some rifles don’t shoot some bullets well.