Weapon (any ammunition), rare
You have a +2 bonus to attack and damage rolls made with this piece of magic ammunition. Once it hits a target, the ammunition is no longer magical.
Applicable Ammunition:
Arrows, Blowgun Needles, Crossbow Bolts and Sling Bullets.
Notes: Bonus: Magic, Damage
So is this magic item like a single arrow/dart/etc? Or is it a pack of ten like you normally get when you buy from a store?
I think its always only a couple.
I think the idea here is you have a couple of these special arrows in your quiver that you pull out for special shots.
But, you are the DM, you could also sell them in packs of (20). That's what normal arrows are sold as.