[Big Friend Ten (BFT)]

Young's Modulus explains that everything is a spring. Lead gives a little upon ignition of the primer and subsequent rapid burning of the powder. It then "springs" back to its original shape. Nice Shot gives less than lead, and steel gives much less so.

Elasticity of solid materials explains why a bridge or tall building sways in the wind without cracking or bending. The more elastic something is the more it will change shape momentarily and then return to its original shape.

As part of the ejecta, the more something gives the less peak pressure will be produced. Different plastic wads also vary in how much peak pressure they contribute to.