A single ammo clip has the following effects on all weapons at these difficulties:
- Very Easy: 40% ammo fill
- Easy: 40% ammo fill
- Normal: 40% ammo fill
- Hard: 30% ammo fill
- Insane: 20% ammo fill
These values are pulled directly from the ME3 coalesced settings file. Note that in the event of a decimal value, it will round down, not to the nearest value. Others, however, have reported that this doesn't necessarily translate to all weapons but I have been unable to confirm this, and it is not in the coalesced settings file that I could see.
Also, it will fill your grenades in the following manner:
- Very Easy: 10 grenades
- Easy: 3 grenades
- Normal: 2 grenades
- Hard: 1 grenade
- Insane: 1 grenade
All guns in need of ammo will receive the full amount of a single reload clip (eg all guns will be refilled by 40% on normal difficulty).
Also note that ammo will respawn given enough time, so if you are really in need of some ammo, camping a spot will can easily refill your gun.