I´ve seen a Replica catapult (a re-enactment group) that fired a 40kg rock over 100 meters (they didn´t put it on full tension because of limited space) but it was roughly half the size the Zvezda model would be if scaled up.
The actual size (it looks big next to a bod) isn´t that far fetched, quite small really...look at this beast!!!
This is a reproduction of a Roman catapult that apparently stood 8 meters tall and weighed 26 tonnes
|If when you build it and take care not to glue the elavation support etc...it can be put into a downward firing position (on a castle wall )...........or......|
|........raised to shoot upwards at a castle wall.|