The topic is about processing damage types, that’s what the system is for - it’s immutable so it should not be used for anything dynamic.
Ammo can be absolutely counted in the WeaponBP, or maybe even ClipBP if you’re dealing with a more complex system. And the clip you hook up to the gun knows its damage type.
Let’s say you’re dealing with a sim-like (Arma) type of game where the player carries multiple ammo clips for various guns, each with different capacity and projectile performance. Each clip should track its own ammo, the gun should only care about what is loaded into the chamber and what to pull the next bullet out of.
Choosing the right tool for the job will depend on the scope. Having a handful of enumerators might be perfectly fine! I was merely suggesting looking into the damage types in case the wires get out of hand… 
Good luck!