This paper studies the ballistic behavior of developed 12.7x99mm armor-piercing (AP) projectiles with Tungsten Carbide Core. The ballistic behavior of the new projectiles has been compared with that of traditional 12.7x99mm AP projectiles. The development of AP projectiles aims to improve their penetration abilities against high-strength alloy steel targets. Three different designs have been suggested and modelled in order to compare the penetration capabilities of them. The study includes the ballistics of the three designs, numerical modelling and simulation, using ANSYS 18 (Explicit dynamics), of the three different projectiles as well as the traditional AP projectile in terms of the determination of penetration capabilities of the projectiles when fired at a steel target with a suitable thickness. The stability of the new projectile designs has been also investigated by using PRODAS software. Two of the three designs are chosen for manufacturing according to the previous study. Finally, firing tests have been performed to determine the penetration capabilities as well as the ballistic performance of the designed projectiles. The results show that the stability has been achieved and the penetration ability for one of the developed projectiles is better than traditional AP projectiles by 1.5 times.