By focusing his Explosion path into a single point, rather than his whole palm, Katsuki is able to produce a concentrated blast that can successfully pierce through solid concrete.
Katsuki performs AP Shot by forming his hand into a circle and places it on his other palm. He then shoots his explosion through the circle in order to keep the attack focused on a fixed point. It was developed during his training at the Gamma Gym. He uses this move to defeat Dictator from above, saving Izuku Midoriya.