Not necessary
18 USC 921(a)(17):
(B) The term "armor piercing ammunition" means- (i) a projectile or projectile core which may be used in a handgun and which is constructed entirely (excluding the presence of traces of other substances) from one or a combination of tungsten alloys, steel, iron, brass, bronze, beryllium copper, or depleted uranium; or (ii) a full jacketed projectile larger than .22 caliber designed and intended for use in a handgun and whose jacket has a weight of more than 25 percent of the total weight of the projectile. In both parts A and B, the regulation is applied to the projectile, in other words, the bullet. Also in parts A and B of the definition, the emphasis is on the use of a bullet that involves a handgun. So the difference between ammunition and armor-piercing ammunition is the designed intent. One describes the intent of the round to be used in a handgun while the other focuses on if that bullet could possibly be used in a handgun. All of this came about with the rise in popularity of AR-15 pistols in which you would still use a .223 round, which is what most AR-15 rifles use. An exception has been made by ATF for certain bullets.