If someone dies from explosive ammo splash, there is no weapon for the message.

My message ended up being:
[player] killed [victim] using their .

Post config
as far as i can see there is no "extra" damage setting other than bullet but you can always try adding it, i dont know whether the plugin can detect what type of ammunition you are using in any given weapon , There are so many variables !

It's not even that I'm concerned with detecting which ammo. The victim dies from the explosion (splash) of the explosive ammo hitting something next to them which results in a message saying they got killed by nothing.