Abstract: To investigate the effects of dislocation distance and projectile diameter on the velocity variation of the second projectile during the sequential penetration of a concrete target, a theoretical model was developed to characterize the energy loss and velocity change during the displaced penetration process. Validation experiments were designed, and a comparative analysis was conducted among theoretical predictions, experimental data, and numerical simulations. The results indicate that displaced sequential penetration reduces the velocity decay of the second projectile, thereby enhancing its penetration depth. As the dislocation distance increases, the beneficial influence of the first projectile on the second projectile’s velocity retention diminishes. Beyond a critical dislocation distance, this effect becomes negligible. A larger diameter of the first projectile corresponds to a greater critical dislocation distance. Under test conditions involving penetration of a 1 m thick C40 concrete target at an initial velocity of 600 m/s, the critical dislocation distances for projectile diameters of 50 mm, 80 mm, and 100 mm were approximately 8d, 10d, and 14d, respectively. The maximum deviations between theoretical predictions and experimental results for the second projectile’s velocity were about 7.1%, while numerical simulations deviated by approximately 3.8% from the experimental data.