Projectile point morphology and penetration performance

Abstract

Prehistoric pointed lithic armatures (used to tip spears, darts, and arrows) vary considerably in mechanically-relevant aspects of their morphology, such as tip cross-sectional shape, cross-sectional perimeter, and cross-sectional area, mechanical advantage, and edge sharpness. The effect of variation in these parameters on penetration performance and lethality, however, is poorly understood. Six 3D-printed points that varied in cross-sectional shape, tip cross-sectional area, tip cross-sectional perimeter, mechanical advantage, and edge sharpness were fired into ballistic gelatin under controlled conditions to evaluate the importance of these variables on point performance. Tip cross-sectional perimeter was found to have the greatest effect on penetration depth in the gelatin, and mechanical advantage was also significantly related to penetration. Cross-sectional shape and tip cross-sectional area were not significantly related to penetration depth, while edge sharpness inversely affected penetration. These results highlight the importance of tip cross-sectional perimeter in the evolution of projectile point design (and reinforce its utility as an indicator of long-range projectile weaponry in the archeological record), but also underscore the multiple constraints that interact when trying to design points to maximize penetration performance, lethality, and durability.