To investigate how different wear levels in the engraving segment of a large-caliber gun affect chamber taper and radial wear deformation, this study analyzes the stress field and interior-ballistic performance under erosive-wear conditions and examines the stress and deformation responses of the barrel and rotating band. Breech pressure is computed from classical interior-ballistic equations; the Johnson–Cook plasticity and damage model (accounting for large deformation, high strain rates, and friction) is adopted; and comparative simulations are performed for four radial-wear scenarios in the engraving segment. Using Abaqus and an explicit dynamic finite-element method, we couple the interior-ballistic equations with the engraving-segment firing process via the VUAMP subroutine. The model is validated against experimental data, and the results are analyzed in detail. The simulations show that, as radial wear increases, the engraving duration becomes longer; the projectile velocity at the end of engraving increases; whereas the velocity at the exit of the extracted barrel segment decreases. Meanwhile, stress-concentration zones shift forward along the projectile’s direction of travel, and the most severe concentration occurs on the driving side at the onset of the rifling land. These findings clarify how bore damage degrades ballistic performance in large-caliber artillery and provide guidance for performance enhancement and life-extension. They also elucidate the mechanisms governing interior-ballistic parameter changes under bore-erosion conditions and offer theoretical references for maintenance strategies.