Idk. Maybe your bs has a base damage of 66 with a bonus of 19 added between 1 and 20 times depending on a roll off between your attack and the mobs ac? 
 
So you do 85,104, 123, 142, 161, 180, 199, 218, 237, 256, 275, 294, 313, 332, 351, 370, 389, 408, 427 or 446 damage depending on whether the roleoff was in your favour)? 
 
I’m sure the system is more complicated than that but it explains the gist of your observations. 
		
		
		
		
		
		
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