This is my sixth try at aiming rules!

Describe your ranged attacks as "aiming" if you want to conserve ammo. The monster is spending hit points to make it harder for you to get a good clean shot in. When you can make a wounding or killing shot I'll let you know and you can just let go of the arrow (which doesn't cost an action but uses the ammo).

Easy-peasy.

Or you can just shoot normally. Which uses ammo.

We'll use the diegesis to make it clear where the arrows and thrown weapons are. If you shoot over an ocean they sink there. If you shoot into an orc's heart it rests there.

The diegesis might also let us know if arrows are broken. Monsters that are not killed may break arrows and bolts using AC or HP. The "mending" spell can fix these. They can't normally break thrown weapons in the same manner unless they have a special ability that lets them do so.