CheckAmmo's and DepleteAmmo's "ammocount" parameter is limited to only DEH ammo it seems. It'd be nice to use this without having to screw with the current AmmoUse properties just to fake it.
Can't do. This would break the entire thing. This parameter is needed to pass default ammo use values for dehacked modifiable weapons to the function via DepleteAmmo and is being used by all of Doom's original attack functions.
...Oh wait a minute, I just realized it's a virtual. I'll just override that and switch the AmmoUse parameters temporarily whenever it's using just primary or secondary for the amounts, run the super function and then swap back.