Interior ballistics modelling of a rifled barrel with cumulative wear effects

Abstract

Background/Aim: Barrel wear progressively changes the interior ballistics of a gun-projectile system during service. In conventional models, its effect is often represented by empirical corrections to chamber volume or resistance parameters, without explicitly accounting for wear accumulation over successive shots. This study develops an interior ballistics model that incorporates cumulative chamber wear as a function of shot count and evaluates its effect on projectile motion in a rifled barrel. Methods: An interior ballistics model was developed by coupling cumulative chamber wear with the governing equations of propellant combustion, gas generation, and projectile motion. Projectile motion was considered in two stages: from cartridge-case separation to complete engraving of the driving band into the rifling, and from engraving to muzzle exit. Wear accumulation was introduced through changes in free-travel distance, effective chamber volume, and gas flow area. The model was applied to a 5.56 mm rifled system using 5.56×45 mm ammunition over a simulated service life of up to 16,000 shots. Results: Increasing shot count resulted in a progressive decrease in peak pressure and muzzle velocity, accompanied by a shift of the pressure peak toward the muzzle. At 16,000 shots, peak pressure and muzzle velocity decreased by approximately 15.6% and 5.1%, respectively, compared with the new-barrel condition. Experimental muzzle-velocity measurements agreed well with the numerical results, with relative deviations of 1.6% - 3.3% over the firing cycle. The axial chamber wear length measured after 16,000 shots was also used to validate the wear parameter adopted in the model. Conclusion: Explicit consideration of cumulative chamber wear provides a more consistent representation of interior ballistics degradation over barrel service life. The proposed model captures the changes in pressure and projectile velocity associated with wear and can be used to assess barrel performance and service life.