This book contains a model of the dynamics of bullet penetration.  This model is technically sound and of general applicability, and represents a significant technical advance over what has been heretofore available.  This penetration model has been derived from general equations of motion, with validation done by, and empirical constants determined from, special tests.  This penetration model is directly related to incapacitation from wound trauma (often called stopping power), a subject that has been of great interest for many decades.  The term used in the book for this incapacitation is WTI, for Wound Trauma Incapacitation; this term refers to the production of an incapacitating wound by the bullet parameters (velocity, weight, shape, diameter), and does not refer to any model of this effect. 

1.  Introduction

2. Understanding Energy Relationships

A tutorial explanation of energy relationships for a nontechnical reader, and does not include a discussion of WTI.  This chapter is included because there is great misunderstanding of all the considerations related to bullet kinetic energy by most individuals interested in WTI.

The interest in bullet effectiveness undoubtedly dates from the earliest use of firearms.  Numerous attempts to quantify bullet effectiveness in a WTI model date back nearly a century; these attempts at quantification are not in mutual agreement, and the dispute among the advocates of various WTI models has waged bitterly and interminably.  The most important of these efforts to model handgun WTI are summarized in this chapter.

The central point at issue in WTI is the relationship between the dynamic and physical parameters of the bullet and the effectiveness of the bullet in live target incapacitation.  There are various and varying physiological and psychological effects of bullet impact on a living body; the complexity of these effects is one of the main reasons why WTI has been so hard to quantify and has been the subject of so much dispute.

The issues related to tissue simulants are discussed in this chapter.  Statistically valid testing of bullet penetration in live targets is very impractical for both obvious and subtle reasons; most of these difficulties also exist for any kind of testing in tissue.  Satisfactory testing must include valid and repeatable testing quantification, and the only practical test medium is an inanimate tissue simulant.

Contains the derivation of the new analytical model of bullet penetration from the general equations of motion.  This derivation is included here for completeness even though many readers will not be willing or able to follow the details of this analysis (which uses calculus and technical terminology).  Following this derivation in this chapter is not critical because the ultimate results are summarized in Chapter 10 in a form that can be used without a detailed understanding of their derivation.  However, reading the text for related information while more or less ignoring the equations is easy and recommended for those not interested in the technical detail.

Uses insights from the penetration model described in Chapter 6 to analytically evaluate the forces on bullets which are penetrating tissue.  The practical interest in this modeling is in assessing and demonstrating the mechanism of bullet expansion as a result of these forces.  A test program designed and implemented to support the analysis by demonstrating bullet expansion and deformation in response to these forces is described.  Bullet deformation testing done by others is discussed and shown to be compatible with the force model.

Summarizes the results of a series of penetration tests made to validate the bullet penetration model of Chapter 6 and to determine some empirical constants in the model.  These empirical test results are in complete agreement with the analytical model derived in Chapter 6.

Summarizes the results of penetration testing and analysis of the effects of bullet penetration through skin.  This chapter describes the issues associated with tissue penetration modeling and the phenomenology of skin penetration.  An analytic model of skin penetration is derived, and test results show this model is valid.

Summarizes the results derived and described in detail in Chapters 6 and 8 in graphs that are understandable and useful to a general reader without technical training.  These graphs allow the reader to estimate the penetration depth that would be obtained in gelatin testing for most common bullet configurations.  JHP bullet penetration depth can be estimated if typical expansion has been determined by firing the bullets into water (expansion in water, gelatin, or tissue is usually similar in well designed JHP bullets for reasons described in Chapters 5 and 7).

Describes the difficulties and uncertainties intrinsic to any model of WTI, highlights why any such model cannot be definitive, and discusses the issues in WTI modeling.  The medical comments from Chapter 4 show that the WTI model should be based on the presumption that WTI is a function of the wound left by the bullet passage; this sounds self evident with this phrasing, but (rather surprisingly) is by no means the usual approach.  The most important aspect of WTI modeling analysis is not a quantitative rating of cartridges, but rather the information it provides on tradeoffs and constraints on bullet design parameters that are independent of the specific rating scale selected (for all WTI scales based on the bullet wound).