Introduction

This document is an improvement of a presentation given by the author at the 1995 AFTE meeting in San Diego, CA (see reference [1]) and a publication in the AFTE Journal (see reference [2]). It is mainly intended for the following readership:

Hunters and sportsmen, having an interest in exterior ballistics,
Students and teachers,
Forensic firearm examiners, especially "newcomers" in the field.

The title of this document "How do bullets fly?" seems to be an odd question, and appears to be almost foolish at first sight..

However, as in many fields of science and technology, studying an apparently simple matter more thoroughly, may bring to light complex and complicated facts. This indeed is the case with regard to the motion of spin-stabilized bullets fired from guns.

Most people expect that bullets fly nose-forward and remain stable from the muzzle to the target, but this is not necessarily so. For short ranges, most trajectories could be approximated by a straight line, whereas bending of the trajectory must be considered for longer ranges.

Most firearm experts accept that bullets may tumble when grazing an object or when leaving an intermediate target. However, as it will be outlined, some physical conditions must be fulfilled to guarantee stable flight, and bullets are by no means automatically stable. Causing a bullet to spin endowes it with gyroscopic properties which are very important - but by no means exclusively - in maintaining bullet stability.

However, from a teacher's point of view, the motion of a spinning gyroscope is one of the most complicated motions with which a student of physics is confronted during lectures on classical mechanics. Although the general motion of gyroscopes can be explained and completely understood only by a thorough mathematical treatment, this introduction makes an attempt to explain the elements of the subject by means of numerous illustrations. The use of formulas is limited to those who wish to see them (note various links to view formulas, indicated by the icon).

For the explanation of some general physical terms used in this article, the interested reader is requested to refer to an elementary physics textbook.

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