I have recently came across information about a mortar, may I reiterate a massive mortar built in 1917 by SKODA at the Štorková engineering works in Brno. This massive 500mm mortar was tested by Germany and Austro-Hungary at the shooting range in Steinfeld and Husovice-u Brna.
One prototype was produced in 1917
The shell weighing in at 270 kg /595 lbs.
Range was 2000m/6561ft.
It name as I understand it was the Storek Mortar System.
If you have any information, please contact me or post it here.
All the Best