The original intention of the 5.45x39 round was a full metal jacket cartridge capable of penetrating light body armor as well as thin barriers. To do so the Soviet round has a full metal jacket (FMJ) over an internal steel core with a lead inlay. The cavity of the round is hollow, but designed not to deform or expand on impact with soft tissue. The 5.45x39 ammo is capable of reaching velocities of 2,900 feet per second. This blistering, but lightweight cartridge allows for a massive amount of penetration against soft flesh.
5.45x39 FMJ ammunition is generally pretty cheap, making excellent practice ammo. The rounds are lightweight, with a standard projectile weight of 53 grains, which makes them quite light and easy to carry in bulk as well. The 5.45x39mm FMJ round is small and lightweight, but was a feared cartridge in the Afghan-Soviet war, and was often known as the poison bullet.