If it hits the target directly, the projectile will bounce straight back at you. Use a cardboard penny as the target, and the copper penny as the projectile. After the collision, the projectile will continue to move, taking the target with it. You have just demonstrated the law of conservation of momentum. Momentum is the mass of an object multiplied by its velocity.
Velocity is speed in a specific direction.
A heavy object has more momentum than a light object travelling at the same speed. An object moving quickly has more momentum than an identical object moving slowly. Unless there is an outside force, such as gravity, acting on an object, it will move forever at a constant speed in the same direction. If it bumps into another object, it will share its momentum with the other object. Both objects may change the direction and speed of their motion, but if you add up the total momentum in any direction, it will be the same as before the collision.