My numbers show that, of 748 killed my firearms in the incidents I have tracked, 267 were killed by "assault weapon" type firearms. That's 36 percent -- just over one-third. So much for the myth that mass shooters overwhelmingly choose AR-15s.
Not doubting your math, but in this case, you're using the wrong numbers.
The number of people killed by "assault weapons" is not the relevant number, when claiming or disproving the claim of what mass shooters choose to use.
the number you need to use is number of times assault weapons were used, against the number of incidents, not the percentage of people killed by a wackjob using assault weapons, or the number of people shot (and survived)
Of course, the resulting number (percentage of times) will depend on the size and accuracy of your database AND the accuracy of your definitions, as well as getting the basic arithmetic correct.
IF, for example, my data base has only 3 incidents, say Stockton (semi auto AK), Louisville (semi auto AK) and Newtown (AR-15), then my statistics will show mass shooters use "assault weapons" 100& of the time! (and FYI the term "assault weapon" did not exist at the time of the Stockton and Louisville shootings).
Now if I add the Virginia Tech murders (handguns), then my result is "mass shooters use assault weapons 75% of the time!!"
Not that it will matter much in the long run. ALL our (misguided?) efforts at getting them to use terms correctly has done is force them to make new terms, defining their incorrect usage as correct.
The next time they redefine "Assault weapon" it might be to the definition many tried to use in the days before the 94AWB.
Some folks (who really ought to have known better) seriously tried to make the argument that ANY gun, and every gun used to assault someone was an "assault weapon".
Grammatically possible in English, but not even remotely
correct usage for the context. It is tempting to consider that it might have been better if we had allowed that definition by use to stand. It would be better, IF they followed the rules, but they won't, so I suppose we're better off the way things are.
IF we accept the definition by use , that a gun is an assault weapon if used to assault someone, they THEY would have to accept the other side of that coin, which is that a gun that has NOT been used in an assault cannot be an assault weapon.
The gun USED in a mass shooting, say an AR type, that gun (ser# bcxya1234) would be an assault weapon because people were shot with it. (shooting people is assault under our legal code), but the AR in my closet, and all the ARs on dealer's shelves, and every where else would NOT be "assault weapons" because they shot nobody, and therefore, would be exempt from and laws or regulations restricting or banning "assault weapons".
The other side won't accept using the definition for individual guns, they demand classification by type, and POTENTIAL evil use, not actual use. And with people of similar outlook writing and passing the laws, they usually get it.