Your calculation is wrong. You are using 4500 miles/second instead of 4500 mile/hour as the velocity. Additionally, small really fast projectiles can more easi

Your calculation is wrong. You are using 4500 miles/second instead of 4500 mile/hour as the velocity. Additionally, small really fast projectiles can more easily pack a lot of kinetic energy relative to a larger, more slowly moving projectile because kinetic energy is proportional to velocity squared. It is not so easy to pack a lot of momentum in a small really fast projectile because momentum is just directly proportional to velocity.