There is a mathematical method, the problem is that we are trying to quantify it in itty bitty units.
We are trying to set the scale in the order of a .22 lr as 1 and the .223 as 5, and so forth, and maybe a 12 guage buckshot round as 9.
what we need to be doing is setting a scale that puts anything short of a .308 as a 0, and a pound of tnt as a 10
once you presume that every antagonist is going to be a 6' 5" 350 pound behemoth hopped up on pcp and wearing full body armor, well, then you can start counting whether or not a .38 special is an effective weapon. Of course, it is a 0 on this scale.
