It's true. I've never seen a shooter take more than about two or three seconds to change magazines when they had a magazine change as part of the drill, and a good shooter does it in less than a second.
Not talking about drills here. Or assuming every crazy school shooter is going to be an expert or function so well in the crisis situation he's created.
I wasn't really talking about overall murder rates, but at any rate rather a lot else has changed since the days of six-shooters so that doesn't tell you a lot.
And it's probably a fallacy to assume every crazy gun shooter will, if he can't be so well armed with guns, will carry out a massacre with explosives. Some will, yeh. But we're not talking perfect solutions here, just what steps can be taken.