Reply To: Why do
Plastics are almost as bad as hard rubber for bouncing pellets back. The primary reason is that the energy of the strike is stored in the plastic as a temporary deformation much like a compressed spring. The plastic springs back sending the pellet on a return trip. Also, the plastic is too soft to allow the pellet to use up all its energy into deformation of the pellet itself, like steel plate does.
Thin spoons also act more like springs and the curved concave surfaces tend to send the pellet back toward the shooter, while convex surfaces will send the pellet off in a diagonal direction. Thick plates, though do indent and spring back slightly, the amount of energy stored is much less since most of it goes to deforming the pellet and sending fragments off to the sides. The spring is too stiff. If the target can indent more, it is capable of absorbing and storing the energy without it disrupting the pellet as much and will send it back with more velocity.