Determination of the Cause of the Differing Ballistic Performance of 9mm DM11 Bullets from Two Manufacturers

In London, firearm threats faced by police during criminal activity include 9mm handguns and submachine guns. The UK Home Office body armour standards have included 9mm DM11 A1B2, manufactured originally by Dynamit Nobel under RWS branding, for over a decade. The recently published 2017 UK Home Office body armour standard continues to specify the 9mm DM11 A1B2, however, the specified manufacturer has changed to Metallwerk Elisenhütte GmbH (MEN). The DM11 A1B2 bullet comprises a copper coated steel full metal jacket with a lead core and bullets from both are specified to the same drawings and dimensional tolerances. However, during empirical testing against soft armour systems differences have been observed in the Vmean measured by CPA for the 2 bullets. As a result, body armour systems designed to pass the standard tests using the RWS 9mm DM11 A1B2 bullet manufactured may have a lesser safety margin when subject to impact with the equivalent MEN bullet. This paper reports on the results of an investigation in to the causes of the differing performance of the two sources of 9mm DM11 A1B2 bullets. It includes a study of the metallurgy of the steel jacket, dimensional and mass comparisons and a range of high strain rate testing to compare the properties and deformation behaviour of the two bullet types. Ballistic tests have been performed to demonstrate how the difference in performance may be related to the observed differences in the steel jacket metallurgy and the resulting differing deformation behaviour. The study has shown that the root cause of the differing performance is due primarily to differences in the steel used for the jackets by the different manufacturers. This work has important consequences for the UK body armour industry and others testing with the 9mm DM11 round.