I support the Second Amendment, I like guns. I was a good shot in the military and still am. But when the Second Amendment was drafted in 1791, the firearm in use was a single-shot musket. It had to be loaded from the barrel with gunpowder, then a ball, and finally cotton wadding was rammed down to the breech. They were, at the time, modern weapons, in that they used a flint (hence the name flint lock) to ignite the gunpowder vs. the old match lock that used a burning "wick" to ignite the powder.
Oh, and they were about 5 feet long. An expert could fire maybe three rounds a minute. ALL firearms (we could exclude the muzzle-loading weapons) should be licensed. And all shooters should be licensed as well, just like getting driver's or pilot's licenses.
We can change the Second Amendment. After all, in 1791 slavery was constitutionally permissible, and we changed that. We changed alcohol rules as well. Twice. We license cars, and no one with an IQ over room temperature thinks the government will sneak into our garages in the middle of the night to confiscate our cars -- and cars are far more dangerous than guns, as they kill more people each year than guns do.
This shooter/gun registration, of course, will not prevent some mental case from massacring people, but it might help.