弾丸の変形に伴う弾径と腔旋痕角の変化

Abstract

Approximately thirty percent of .38 caliber revolvers seized in Japan are home-made guns called Paltik which were made in Cebu Island, in the Philippines. Bullets fired from Paltik have the following general characteristics; (1) Rifling mark is rough and unclear because of crudely finished rifling of bore. (2) Bullet is elongated because bore diameter is usually smaller than specified value. With the improvement of the manufacturing skill of Paltik nowadays, it has become difficult to distinguish that were fired from Paltik and an authentic gun based on the characteristic indicated in (1). When the rifling mark of a bullet in question looks neat, the characteristic indicated in (2) becomes critical to identify make of the firearm. As evidence bullets usually deform to some extent, it is necessary to clarify the rate of diameter change in deformed bullets. In this study, .38 Special bullets were shot into thick steel plate, concrete blocks and polycarbonate plate at a right angle from a Smith & Wesson revolver and the following results were obtained: A) The diameter in the base of lead bullets which were impacted into a thick steel plate was contracted up to 7.4%. B) The angle of twist of the rifling mark was reduced from 21% to 24% when lead bullets were impacted into a thick steel plate or concrete blocks.