You could let it check what type the hitted thing is.
%colType = %col.getType(); //%col changes to CorpseObjectType if you kill a player
if(%colType & $TypeMasks::put_a_TypeMask_here)
TypeMasks:
Raycasting bricks: $TypeMasks::FxBrickObjectType
AI/Players: $TypeMasks::PlayerObjectType
Static shapes $TypeMasks::StaticObjectType
Terrain: $TypeMasks::TerrainObjectType
$TypeMasks::VehicleObjectType
This is from the support script from raycasting stuff, but it can also be used with:
function PutProjectileNameHere::onCollision(%this,%obj,%col,%fade,%pos,%normal)
Then you can use the above to let it play a sound in the right circumstances, like when you hitted a player/wall/whatever.