• Alison Lyall, D J Carr, C Lankester, and C Malbon.
• Impact and Armour Group, Centre for Defence Engineering, Cranfield University at the Defence Academy of the UK, Shrivenham, UK.
• J R Army Med Corps. 2017 Feb 1; 163 (1): 35-38.

IntroductionSome military specialists wear body armour that is more similar to police armour and provides protection from ammunition fired from pistols. During ballistic testing, these armours are mounted on a standardised type of modelling clay and the back face signature (BFS; depth of depression) formed as a result of the non-perforating impact event on to the armour is measured. This study investigated the effect of impact angle on the BFS and on the deformation of the bullet.MethodsTwo commonly worn types of armour (HG1/A+KR1 and HG1+KR1) were considered that provide protection from pistol ammunition and sharp weapons. Armours were tested against two types of pistol ammunition (9 mm full metal jacket and 9 mm hollow point) at eight different impact angles (0°, 15°, 30°, 45°, 60°, 70°, 75° and 80°).ResultsIncreased impact angles resulted in smaller BFSs. Impact angle also affected whether bullets were retained in the armour; as the impact angle increased, the probability of a round exiting the side of the armour increased. Bullet deformation was affected by impact angle.ConclusionsUnderstanding the deformation of bullets may assist with recreating a shooting incident and interpreting forensic evidence.Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/.

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