AFTE Store - Reading Primers

Gun writers, ammunition reloading manuals and a few forensic firearms examiners who deal with firearm bursts and failures have all described certain signs of excessive pressure hich may be expressed in the primer of a recovered cartridge case. These signs can be valid, but only after a thorough evaluation and understanding of the characteristics and behavior of the specific firearm/ammunition combination are established.

In this study, cartridges in six popular calibers, .380 Auto, 9mm Luger, .357 Magnum, .40 S&W, .45 Auto and .223 Rem, were handloaded with incrementally increasing propellant charges to ultimately produce calculated peak pressures typically in excess of 80,000 psi (550000 kPa) as determined by the QuickLoad™ program. The actual peak pressures were measured with test barrels equipped with piezo transducers and an Oehler M83™ pressure-velocity system. This allowed a comparison between the QuickLoad™ calculations and the measured values as well as an assessment of the accuracy of the QuickLoad™ program in predicting muzzle velocity and peak pressure values.

The central purpose, however, was to study and photograph the breechface markings in the fired primers and to measure the firing pin impression depths for each powder loading level when these specially loaded cartridges were fired in actual firearms. These loadings also allowed for a study of the completeness, the character and clarity of detail of breechface impressions at known peak pressure values.