D&D 5E Magic Ranged Weapons and Magic Ammunition

[CapnZapp]

Right, but let's say I hit 7 times out of 10. The simple part is figuring out I recovered 5 pieces of ammo, aye. It's also easy to see that only 3 pieces of ammo are still magical.

The question I was trying to ask is, how do we determine how many of those 3 still-magical shots do I actually recover?

The rules leave that up to you.

Being generous and say "you'll recover any magic ammunition that missed up to a maximum of half the total fired shots" is entirely reasonable if you ask me.

You could make it more complicated. I wouldn't.