Mentsch1 – Your first post, drawn from Wikipedia, has some good points. Those are all factors, especially the copycat issue, since a lot of mass shooters were obsessed with previous killings. However, the number of guns has gone up, and the types of guns have skewed toward the lethal assault-type. (I’ll try to get you cites on that. I’m a registered Wikipedia editor 🙂
Second post: the current official difference between assault and non-assault rifles was a political compromise, not a practical judgment. It was hammered out in the conference rooms of Congress in an attempt to get the legislation passed in spite of the gun industry. (I was following it when it happened – just after the assassination attempt on Pres. Reagan.) What we need is a ban on civilian ownership of any gun that is or could be converted to automatic or semi-automatic. Combat weapons belong in the hands of the military and the police, not well-meaning but untrained civilians. Unless you’re a white nationalist who thinks he has to defend himself against the government, a plain old rifle or shotgun is going to kill your deer or your home intruder just fine.