In Quantitative Ammunition Selection, Charles Schwartz presents an accessible mathematical model that allows armed professionals and lawfully-armed citizens to evaluate the terminal ballistic performance of self-defense ammunition using water as a valid ballistic test medium. Based upon a modified fluid dynamics equation that correlates highly (r=+0.94) to more than 700 points of manufacturer- and laboratory-test data, the quantitative model allows the armed professional to generate ballistic test results equivalent to those obtained in calibrated 10 percent ordnance gelatin. Using data generated from water tests, the quantitative model accurately predicts the permanent wound cavity volume and mass, terminal penetration depth (+/- 1cm), and exit velocity of handgun projectiles as these phenomena would occur in calibrated 10 percent ordnance gelatin and soft tissue. A retired law enforcement professional, Schwartz provides a concise explanation of the relevant principles of mechanics, fluid dynamics, and thermodynamics pertaining to the model and its derivation. The quantitative model is clearly presented with illustrated computational examples that provide guidance to the armed professional in every aspect of the model's application.