Two factors limit penetration in very high velocity impacts with cup in core bullets. First,penetration is a function of momentum and bullets lose momentum as they shed mass.
Second,cup in core bullets tend to expand to very large frontal areas which creates more friction and limits penetration.
In a monolithic bullet,mass loss is very limited,and the frontal area may get smaller as the bullet continues to expand. The net result is that penetration can increase with velocity because they maintain their momentum and have smaller frontal areas that penetrate with less friction.
