It seems that direct weapon cost (without decay) determines loot. Till now I've assumed that it is hp dmg done.
As it looks now, mobs do record dmg cost (ammo, without decay and misses) and pays out accordingly.
P.S. This might also expalin why I had unknown variability when trying to establish a loot model for hunting. The data I've used was from different weapons.
How about melee? And why you rule out the misses?