A projectile assembly comprises a base portion for receiving projectiles such as slugs and has an associated pusher plate at a rear end thereof for minimizing or controlling deformation of the rear end of the base portion during firing. The pusher plate has a disc with one or more axially extending projections that extend axially into the rearward end of the base portion thereby reinforcing the base portion and upon firing providing uniform axial deformation and/or obturation of the base portion with respect to a firearm barrel. The projectile assembly may be, for example, part of a shotgun shell slug cartridge, and provides enhanced accuracy over the prior art.