[Rupert]

One of the things that make musket shots so dangerous is their size, which gives them pi+ or pi++ damage. If you want to emphasise armour's value, your idea of giving them AD (0.5) is a good one. If you want to simply reduce their lethality, making them do crushing or pi damage is probably more useful. Crushing makes them very effective vs zombies, so if that's something you don't want, make them pi, but note that pi attacks can target the vitals and eyes, whilst crushing can't, but crushing has better knockback and blunt trauma so choose the dame type that has the effects you most want.