The swinging handle pushes the punch against the steel spring's return pressure - the punch travels in a path diagonal to the flat surface of the primer

As the chisel tip of the punch meets the primer's surface, it catches it and pushes it into the cavity in the case head, deforming the primer and dislodging it from the primer pocket

Slick and simple

I use a seating die threaded into the press upside down to hold the case head-up and with a hand held small chisel tip punch and a light mallet I preform the same task

Too easy