That’s interesting as I was reading this article earlier, and they say that AP rounds will drop unhelmeted / unarmoured enemies if you hit them in the head (but sponge otherwise).
Far Cry 6 adds a new ammo feature. It’s a bit annoying. Just stick to using armor piercing rounds. You can craft and equip these via any workbench you find out in the world. If you go for headshots, armored rounds will drop helmet-wearing soldiers as well as unarmored baddies too. The only problem is if you don’t hit someone in the head or shoot something not wearing armor (like a dog), as it can take many more AP rounds to kill them. Does this make any logical sense? Not really, but here we are. So always keep a gun with standard or soft target rounds. We suggest an assault rifle or SMG, something that can take care of groups of dogs and soldiers in a few seconds.