title: Inconsistency in 9 mm bullets: correlation of jacket thickness to post-impact geometry measured with non-destructive X-ray computed tomography.
abstract: Fundamental to any ballistic armour standard is the reference projectile to be defeated. Typically, for certification purposes, a consistent and symmetrical bullet geometry is assumed, however variations in bullet jacket dimensions can have far reaching consequences. Traditionally, characteristics and internal dimensions have been analysed by physically sectioning bullets--an approach which is of restricted scope and which precludes subsequent ballistic assessment. The use of a non-destructive X-ray computed tomography (CT) method has been demonstrated and validated (Kumar et al., 2011 [15]); the authors now apply this technique to correlate bullet impact response with jacket thickness variations. A set of 20 bullets (9 mm DM11) were selected for comparison and an image-based analysis method was employed to map jacket thickness and determine the centre of gravity of each specimen. Both intra- and inter-bullet variations were investigated, with thickness variations of the order of 200 μm commonly found along the length of all bullets and angular variations of up to 50 μm in some. The bullets were subsequently impacted against a rigid flat plate under controlled conditions (observed on a high-speed video camera) and the resulting deformed projectiles were re-analysed. The results of the experiments demonstrate a marked difference in ballistic performance between bullets from different manufacturers and an asymmetric thinning of the jacket is observed in regions of pre-impact weakness. The conclusions are relevant for future soft armour standards and provide important quantitative data for numerical model correlation and development. The implications of the findings of the work on the reliability and repeatability of the industry standard V50 ballistic test are also discussed.
authors.affiliation: WMG, University of Warwick, CV4 7AL, United Kingdom. Electronic address: john.thornby@warwick.ac.uk.
authors.forename: John
authors.initials: J
authors.lastname: Thornby
authors.affiliation: Simpact Engineering Ltd, Unit 5, Benford Court, Lower Cape, Warwick CV34 5DA, United Kingdom.
authors.forename: Dirk
authors.initials: D
authors.lastname: Landheer
authors.affiliation: Simpact Engineering Ltd, Unit 5, Benford Court, Lower Cape, Warwick CV34 5DA, United Kingdom.
authors.forename: Tim
authors.initials: T
authors.lastname: Williams
authors.affiliation: Metropolitan Police Service, Operational Technology, 8-20 Loman Street, SE1 0EH, United Kingdom.
authors.forename: Jane
authors.initials: J
authors.lastname: Barnes-Warden
authors.affiliation: Metropolitan Police Service, Operational Technology, 8-20 Loman Street, SE1 0EH, United Kingdom.
authors.forename: Paul
authors.initials: P
authors.lastname: Fenne
authors.affiliation: WMG, University of Warwick, CV4 7AL, United Kingdom.
authors.forename: Danielle G
authors.initials: DG
authors.lastname: Norman
authors.affiliation: WMG, University of Warwick, CV4 7AL, United Kingdom.
authors.forename: Alex
authors.initials: A
authors.lastname: Attridge
authors.affiliation: WMG, University of Warwick, CV4 7AL, United Kingdom.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Williams
keywords: Ammunition variability; Armour standard; Ballistic impact; Bullet geometry; Jacket thickness; X-ray computed tomography