Surface damage from perpendicular and oblique bullet impacts in stone

Abstract

Controlled experiments were conducted to investigate the surface damage caused by perpendicular and oblique impacts of bullets into sandstone and limestone targets. Individual bullets fired in conditions simulating modern rifles at typical combat distances excavated craters with diameters from 22 to 74 mm and depths from 3 to 24 mm. Limestone target craters were up to twice as large and deep as those in sandstone. These craters have a complex shape consisting of a central excavation surrounded by a shallow dish, compared to the simple bowl shape of most sandstone impacts. Radial fractures extending to the edge of the target block were common in limestone targets. Impacts at an angle of 45° to the surface in both rock types result in asymmetric craters. Two common types of intermediate cartridge (ammunition) were compared: the steel-tipped 5.56 × 45 mm NATO projectile generally produced larger and deeper craters than the 7.62 × 39 mm projectile that is commonly fired from AK-47 rifles, despite having approximately half the mass of the latter. These results characterize the sort of damage that can be expected at many sites of cultural significance involved in contemporary conflict zones, and have important implications for their conservation: for example building stone with low tensile strength is likely to sustain more damage and be at risk of greater deterioration.

Subsurface fracturing of sedimentary stones caused by bullet impacts

“…The sandstone sample (SRS_09) has a shallow, bowl shaped crater with an area equivalent diameter of 40 mm and a maximum depth of 5.1 mm [ 24 ]. 20 mm directly below the crater floor is an open (<1.5 mm) fracture that is 16 mm in length, but does not reach the edge of the section ( Fig 3a ).…”

Bullet ricochet mark plan-view morphology in concrete: an experimental assessment of five bullet types and two distances using machine learning

“…The application of different methods (e.g. geometric morphometrics; deep learning) and impact depth topography [ 33 ] will likely enhance classification rates and identification of ricochet marks further. The morphological assessment of ricochet impact marks from different distances (closer, longer) velocities (faster, slower), incident angles (steeper, less steep), bullet types (e.g.…”

“…For example, Campbell et al. [ 33 ] showed morphological differences in terms of crater depth and topography of 5.56 mm × 45 mm NATO bullets ( n = 18) and 7.62 mm × 39 mm (AK-47) bullets ( n = 18) in limestone and sandstone at 90° and 45° incident angles. Nishshanka and Shepherd [ 47 ] documented a negative correlation in which the length of ricochet mark in wood decreased when the angle of incidence increased.…”

“…Previously, researchers have depicted or described experimental bullet ricochet impact marks in materials like wood [ 30 ], sheet metal [ 8 ], ceramic tiles [ 9 , 31 ], concrete/cement [ 32 ], sandstone and limestone [ 33 ], gypsum wallboard [ 34 ] as well as automobile ceilings [ 35 ]. In some cases, interesting morphological features have been identified that may be indicative of particular bullet types (e.g.…”

“…In still other cases, researchers have explored crater depth and ricochet mark diameter in different materials at different impact angles, e.g. in sandstone and limestone at 90° and 45° [ 33 ].…”