Military type weapons, like an AR15 or AK47, automatic or semi-automatic, do incredibly devastating damage. They do since they are designed as military war weapons where the users of them, typically soldiers fighting other soldiers. A wound which would be in no way lethal from a 'regular' rifle or a 'regular' handgun can be easily lethal and deadly when fired into a victim from a shooter using these military type weapons. Getting hit with a round from these types of weapons is like having an explosion going off in your body. As a semi-automatic, they are capable of firing as quickly as the shooter can pull the trigger, typically 2 rounds per second. If automatic, they can fire a blistering hail of death. These type of weapons have no place in the hands of anyone other than the military and police.
That would be great.
And yes, they are for mass killing, no other reasons.