Long Range Hunting Online Magazine

Ballistics and Predictions

Ballistics and Predictions

By Gustavo F. Ruiz
http://www.patagoniaballistics.com

Long Range is all about ballistics. Beyond that, no more than luck can be expected without it.

Background

About a year ago, the Lapua company released aerodynamic data for some of their bullets. However this time the numbers were based on measurements taken by Doppler radar. Itís important to note that no public details were given in regards of the equipment and configuration used to take the measurements and post processing.

Doppler radar is, without a doubt, the most reliable method known to ballisticians to obtain in-flight aerodynamic data. Doppler radars are used to acquire exact real world data on the flight behavior of bullets. From the collected data points, through a process called Data Reduction, Lapua derived Coefficient of Drag curves, from which BC and other important parameters were calculated then referenced to the ICAO Standard Atmosphere, in order of make these numbers useful for post processing in ballistics programs.

Since the sole objective of ballistics programs is to predict downrange trajectory parameters, a good friend of mine asked me to compare the output of LoadBase 3.0 to a well established baseline. This was difficult to do since serious baselines do not easily reproduce out there. I thought that a baseline should be verifiable and of course, based on trusted facts. For that reason I chose to rely on the data supplied by Lapua as a baseline, because it meets the two aforementioned objectives: itís public and itís based on radar measurements.

Granted, comparisons are by nature good food for dispute, and I like that a lot. In fact, I know there are many questions that could remain unanswered, but I prefer to keep this article as simple as possible in order to avoid any mathematical complexity which could prevent reaching a large audience. Iím the first one to acknowledge that more scenarios are needed to obtain in-depth conclusions, but the baseline data Iím using has its restrictions. Nevertheless, simplicity in both the presented data and conclusions is by no means any indication of an inaccurate concept or biased conclusions.

Unfortunately the data supplied by Lapua does not include transonic/subsonic data, since the dataset used for the assessment is limited to 1000 yards, and this cartridge/bullet combination reaches the subsonic threshold at about 1600 yards.

Even under this limitation, the evaluation is quite useful to show some aspects of the different approaches taken by the most common ballistics engines in use, which is in the last instance the main purpose of the article.

The Baseline Dataset & Ballistics Methods

For those interested, the flyer with the information used here as the ďbaseline dataĒ can be downloaded at:
http://www.lapua.com/fileadmin/user_upload/esitteet/338LapuaMagnum2010.pdf

The reference used is the Imperial units chart, and all the calculations were based on the following parameters.

Ballistics and Predictions

Itís significant to realize that the BC-G7 is a calculated value, resulting from a conversion made using the ďAnalyzerĒ module of LoadBase 3.0. Lapua does not provide other value than the G1 reference. As can be verified the other parameters values are taken from Lapuaís chart ďas isĒ.

The following charts shows two ballistics results, Velocity & Path, where each one is compared to Lapuaís data against the predictions made by LoadBase 3.0, the Point Mass and Pejsa methods, both of which are well established in the shooting community.

The graphs are based on the arithmetic difference between the baseline data and the corresponding predictions as yielded by the different engines. While itís possible to perform other statistical analysis, I found no sensible reason to do that. For the objective of the article, there is no need to complicate matters.

Just for the record, without reliable data no ballistics engine in the world can adapt itself to match field data. Tweaking is not a recommended general procedure, unless the shooter is very knowledgeable and is 100% sure of what parameter needs to be adjusted from the published values.

In short, how one can be sure that the value to modify is the BC? Why not the Zero Range, the Sight Height or the Muzzle Velocity? What about the environment conditions?

Some are non-linear parameters and most of the time, tweaking them will make for a certain point along the trajectory while the other results will become twisted at other range. Be careful, when it comes to adjust the input and be sure that the collected field data can be trusted.

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