i seems to be impossible to have speed above 320m/s. it is also stated in game files that cartriges are not compatible with fuze charges. so i could just mess with mod files so it allowes to have multiple cartriges at once and have more speed? it doesn't seem fair
Speeds over 320m/s were absolutely possible, as this cannon shot at 400m/s and with mods and config changes you can make shells over 320m/s.
I don't know what a "fuze charge" is but if you mean "powder charges" then those were absolutely compatible with cartridges, as long as the cartridge was at the very back and one of them were loaded.
Unfortunantly over a year and a half has passed since I developed this artillery piece and since them the ability to shoot both powder charge and cartridges has been revoked. (Bear in mind that not all ponders existed back then)