The emergence of stone-tipped projectile weaponry was an important event in hominin evolution. A common archaeological approach to identifying projectile weapons is to extrapolate from optimal values of ballistically-relevant attributes as determined from ethnographic North American weapons and modern experiments. Among the most significant of these attributes is "tip cross-sectional area" (TCSA) because it determines a point's efficiency in penetrating an animal. The warranting argument for projecting these data onto prehistoric artefact's is that past "research and development" necessarily led to stone projectiles with optimal TCSA values for a given delivery system. However, our test of this warranting argument, involving analysis of 132 hafted ethnographic Australian stone projectile points and 102 hafted knives, demonstrates that Aborigines did not optimize TCSA values, thus offering a challenge to TCSA-based narratives about the first appearance of projectile weaponry. This illustrates the difficulty of inferring ancient stone workers' design intentions from narrowly-defined optimal values. Instead, tool designs should be considered in the context of the reduction sequences that produced them and the dynamics of transmission of those reduction sequences across generations.