I don't no if anyone needs this but heres how to get any calliber for the cannon part you want.
First you need to open the xml edit
Then got to the dropdown menu and go to cannon
Find the diameter value
1mm = 0.002
Multiply 0.002 by the desired calliber (in mm) then set diameter to that number. Have a nice day.
For example for a 37mm cannon you use 0.074
@Jayden412 thank sir. you are a hero
@Tookan I know This forum Is for people who need it or didn't know already.
I think most of us know that already but ok