1) Are metal cartridges "alchemical cartridges" (and thus reduce the reload time)?
They are described as such, but not listed on the table or under the alchemical cartridge text.
Yes. they are a type of alchemical cartridge if i remember correctly.
Can you make sense of why they have their own separate entry?
So the developers decided to write that a revolver (an advanced firearm) requires a move action to reload (albeit completely) with it normal ammo - metal cartridges which are described as alchemical and thus reduce that reload time by one step to free rather than just state that its a free action to reload? It seems counter-intuitive.