Inconsistency in 9 mm bullets measured with non-destructive X-ray computed tomography

Fundamental to any ballistic armour standard is the reference projectile that is to be defeated. Typically, for certification, consistency of bullets is assumed. Therefore, practical variations in bullet jacket dimensions can have far reaching consequences. Traditionally, internal dimensions could only be analysed by cutting bullets which rules out any subsequent ballistic assessment. Therefore, the use of a non-destructive X-ray computed tomography (CT) method is explored in this paper. A set of 10 bullets (9 mm DM11) was taken for analysing both intra and inter bullet jacket thickness variation. CT measurements of jacket thickness were validated with high resolution scanning electron microscope (SEM) images. An image based analysis methodology has been developed to extract the jacket thickness map and the centre of gravity. Thickness variations of the order of 200 μm were found commonly across all the bullets along the length and an angular variation of up to 100 μm was found in a few bullets. Jacket thickness and centre of gravity were also calculated for the same bullets after impact and the variations between the pre- and post-impacted bullets were compared, by establishing a common physical reference. The results show that the proposed CT scanning approach and subsequent image analysis method can bring out the statistical variations in bullet geometry pre- and post impact effectively.