The 10 cm PAW 600 - later re-designated 10H64 - was a lightweight anti-tank gun that utilized a high-low pressure system to fire hollow charge warheads (and most likely high explosive and smoke shells).
By 1943 it was becoming obvious to the German army that conventional anti-tank gun design had reached its practical limits. Traditional high-velocity guns that relied on kinetic energy to defeat heavily armored targets were becoming so bulky in order to deal with the new generation of tanks that they were becoming too heavy for front line use, and too expensive to produce.
Rheinmetall Borsig

Rheinmetall

Rheinmetall AG is a German automotive and defence company with factories in Düsseldorf, Kassel and Unterlüß. The company has a long tradition of making guns and artillery pieces...

 proposed a new medium velocity gun with a smoothbore barrel that relied on hollow charge ammunition to defeat tanks.