Hi !!!
I think you should look at your first post about fighter bomb load.
As far as 20mm Madsen cannon is concerned you sould try at the link :
http://www.winterwar.com/Weapons/FinAT/FINantitank.htm.
According descryption, 20 PstK/40 cannon is the one you are looking for.
The technical data is included.
Best regards