There are two possibilities for pellet deformation, barrel scrub aside. One is due to acceleration and the other is due to pellet to pellet contact. Deformation is caused by force per square inch above the pellet material's compressive yield strength. Spherical contact points are very small, so relatively smaller forces will cause an "upset" spot on both spheres. As the upset spots grow and the material work hardens, relatively higher force is required to continue to grow the spots.
IMO, (no, I've not done the math) upset occurs only from pellet to pellet contact and only near max pressure. Pellets are deformed as the pressure passes through max chamber and then deformation stops for the rest of the ride down the barrel. I do not believe there is sufficient acceleration to deform the pellets from MA.
DDA
