I know this comes a bit late, but i just stumbled over it when i set up my UP 6.9.
In the \vampire\cfg subdirectory is a file called skill1.cfg
You can open it with a simple text editor. There is a block weapons with entries like this one:
The last line is the amount of spare ammo you can carry for this weapon. So you should use a multiple of the weapon's capacity.
Tuesday is Soylent Green day.