it helps very little, but try from different angles, or even from above a bike or bycicle you might or not be able to get it, at least usually works with some other items arround the map that have the same issue.
It works like in real life. Learning by doing.
You earn ammo crafting points by crafting ammo. The ones in the world are just a bonus and are just there as replacement for the previous crafting schematics that where there.