So first of all let's identify the cause of the issue:
Restriction on the type of caliber is not going to minimize this type of insane massacre. The individual sick in the brain to kill small children could have accomplished the same using a mere .22 caliber pistol or rifle, which can be founs easily with or without stricter gun controls. Moreover, one can make the case that an idiot like that could choose his car to kill as many children or people in a busy street.
That said, we need security staff with powerful rifles on every single 'gun free zone' institution.
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