Analysis of twist-rate effects in a progressive-rifling barrel using finite element method

In this study, a nonlinear finite element model of a 30 mm chain-gun barrel with progressive rifling was developed to investigate the influence of twist-law parameters on interior ballistic behavior and rifling-induced stresses. The progressive twist design was characterized using the twist exponent n and the muzzle exit angle ${\alpha }_E$. Their effects on projectile translation, spin evolution, and rotating-band engraving stresses were evaluated. The results reveal that muzzle velocity and axial acceleration are governed primarily by chamber-pressure loading and are largely insensitive to the rifling-geometry variations considered. In contrast, the twist exponent has a pronounced influence on spin-rate growth and on circumferential ($\theta$-direction) stresses induced by rotating-band engraving. Circumferential stress exhibited strong sensitivity to twist intensity, with variations exceeding 30%, indicating that progressive twist design directly controls stress concentrations along the rifling lands. Among the examined cases, n = 1.6 produced a comparatively balanced stress response and stable spin-rate development. Based on a combined assessment using finite element stress analysis and the Miller gyroscopic stability criterion, a design range of n = 1.6 and ${\alpha }_E$ = 7°-8° is recommended to achieve adequate gyroscopic stability while limiting excessive engraving stresses. The proposed modeling framework provides a quantitative basis for optimizing progressive-rifling barrels under high-pressure interior ballistic conditions.