It's the combination of high muzzle velocity with a semi-automatic weapon that is particularly lethal. If we restricted semi-automatic weapons larger than 22 ca

It's the combination of high muzzle velocity with a semi-automatic weapon that is particularly lethal. If we restricted semi-automatic weapons larger than 22 caliber, that would likely greatly reduce the number of fatal injuries in these mass shooting events. It's going to slow the shooter down having to reload each shot. But: most gun homicides in America happen with handguns. So you'd be banning an entire class of weapons in order to save a relatively small number of lives. Obviously we've drawn some lines where we consider some weapons too lethal: no one gets to own fully automatic weapons. Or hand grenades. So we'd be deciding that semi-automatic high velocity weapons fall into the "too lethal" category. It wouldn't prevent mass shootings - but it would make events like Las Vegas less lethal. (Of course, there's the separate problem of preventing the newly banned weapons still in circulation from ending up in the hands of would-be mass shooters.)