Abstract: To clarify the thermomechanical coupling mechanism and improve the assessment of ignition response of melt-cast charges under bullet impact, a DNAN-based RL-1 melt-cast cased charge was investigated in this study. A series of 12.7 mm bullet impact tests and corresponding numerical simulations were conducted to investigate the thermomechanical response and ignition behavior of the charge at different impact velocities. A method for calculating the extent of reaction at high-temperature nodes was proposed based on temperature reconstruction of failed elements. High-temperature nodes near the penetration channel were screened, and their extent of reaction was calculated using the Arrhenius kinetic equation. The results show that, at an impact velocity of 850 m/s, the bullet penetrates the aluminum casing and causes mechanical fracture of the charge along the penetration direction. The high-temperature region is mainly concentrated near the penetration channel; however, the hotspot duration and accumulation of the extent of reaction are insufficient. The extent of reaction at all high-temperature nodes remains below λ=1, corresponding to a critical reaction volume fraction η of 0. When impact velocity increases to 1000 m/s, the local friction and shear effects near the penetration channel are enhanced. The extent of reaction at some high-temperature nodes reaches λ=1, and these nodes are identified as critical nodes, with η=0.39%, indicating that local regions of the charge have reached the condition for reaction instability. The numerically predicted trend of enhanced local reaction is generally consistent with the experimental observations. As impact velocity further increases from 1000 m/s to 1300 m/s, friction along the penetration-channel wall and shear-induced plastic heating are intensified, the number of critical nodes increases, and η exhibits an overall increasing trend, indicating that the local reaction region expands with increasing impact velocity. These results demonstrate that increasing impact velocity intensifies the conversion of mechanical energy into thermal energy near the penetration channel, increases the number of local critical nodes, and promotes the accumulation of the extent of reaction.