I've found using an item with ammo always consumes 2 ammo. I have the following setup:
[Artifacts] Item use always uses 2 ammo
Code:
ThrowingDagger:
Id: 262
Data: 0
Display: 'Throwing Dagger'
Resource: Ammo
Ammo:
Enabled: TRUE
Bullet: Ammo-ThrowingDagger
ClipSize: 13
Lore:
- '&7Ammunition 13 / 13'
- '&7Durability 180 / 180'
Skills:
- skill{s=ThrowDagger} @TargetLocation ~onUse
- skill{s=ThrowDagger-Reload} @self ~onSwing
Ammo-ThrowingDagger:
Id: ink_sack
Data: 1
Display: '&fThrowing...