Numerical Investigation of the Aerodynamic Characteristics of a .40 S&W JHP Bullet

The external-ballistic behaviour of a projectile is governed by the drag forces acting on it throughout flight; accurate prediction of the drag coefficient (Cd) is therefore critical for trajectory and range calculations. However, the drag coefficient of the .40 S&W JHP bullet has not been reported in the literature and its open hollow-point nose is not represented by the standard drag-law families that assume conventional ogival profiles. This gap is compounded by the operating velocity of the round (352 m/s, Mach ≈ 1.02), which lies in the transonic regime, where shock formation and base separation make the drag coefficient particularly difficult to estimate. To address this gap, this study determines the drag coefficient of the .40 S&W JHP bullet through a three-dimensional Computational Fluid Dynamics (CFD) external-flow analysis based on NIJ 0101.06 reference conditions. The simulations were performed in ANSYS Fluent under the ideal-gas assumption, using the k-ω SST turbulence model with a wall-resolved near-wall mesh (y⁺ ≈ 0.94) and a grid-independence study. The numerical analysis yielded a drag coefficient of Cd = 0.255. The flow field exhibited a pronounced pressure difference between the high-pressure stagnation region at the nose cavity (≈ 1.09×10⁵ Pa) and the low-pressure wake behind the base (≈ 4.39×10⁴ Pa), while the local Mach number reached 1.39 at the nose, indicating shock-wave formation; these results show that pressure drag is the dominant component of the total aerodynamic resistance. The original contribution of this work is that it provides, for the first time, a geometry-specific Cd for this widely used round in the transonic regime and quantifies the influence of the hollow-point cavity on its drag behaviour. The reported value provides a reference for external-ballistic trajectory prediction and for the design of ballistic test setups relevant to body-armour evaluation.