The standard “ball” bullet used by the Russian military, at least, in the 5.45x39mm is designed to easily tumble once it is inside the target. It is more of an effect of the bullet’s construction and fine tuning of the rifling twist rate than the caliber itself. But it is still supposed to remain stable with the nose pointed forward when traveling to the target. Otherwise it becomes extremely inaccurate and loses its velocity very rapidly, which causes it to fall short.