Why can't an ammo be made as multiple types in latest experimentals?

Originally gasoline could be used as flamethrower fuel, and 380 can be put into 9x19 guns. This was because for the ammo_type field allowed multiple entries. Why does this not work anymore?

Rework? i guess. i mean, is not a bug, flamethrower has to be napalm and there is a recipe for homade napalm too (or whatever is called). Even the rocks got it code reworked