Aiming at the unclear issues of charge deformation and ignition mechanisms in the spigot safety evaluation tests of cast explosives， a viscoelastic-viscoplastic deformation and multi-hotspot competitive ignition model for cast PBXs was developed. This model considers multiple hotspot mechanisms， including microcrack friction， microvoid collapse， and localized viscous shear flow heating. Simulations of macro-mesoscopic rheological-ignition response under spigot were conducted， obtaining the pressure， shear flow， and ignition response characteristics of explosive charges under different drop heights， spigot lengths， and spigot shapes. The results indicate that the ignition response process of the charge under spigot is driven by both pressure and shear strain rate. When these two factors overlap at high levels， the resulting localized viscous shear flow becomes the dominant hotspot mechanism. For the same spigot diameter， a larger aspect-ratio spigot induces higher pressure and shear flow in the charge above the spigot， coupled with a longer spigot action time and higher impulse， leading to an easier ignition with a reduced critical ignition height. Compared to a flat-head spigot， an oval-head spigot significantly reduces the critical ignition height of the charge. These findings provide technical support for interpreting the ignition response and mesoscopic mechanisms of cast explosives under low-speed long-pulse penetrating mechanical stimulation， as well as for constructing safety evaluation and numerical characterization methods for projectile drop with foreign object penetration.