First, I think you mean "semi-automatic" weapons, since automatic weapons are exceedingly difficult to obtain, require special background checks, registration and licensing, and are also exceedingly expensive because there are relatively few of them in existence.Also sad: sales of automatic weapons have increased since Newtown.
Second, sales of all sorts of guns and ammo, including semi-automatic handguns, always increase considerably when the drumbeats of the gun-grabbers start up again. I know of at least two shops that are currently sold out of anything worth buying, but both of Obama's wins also increased sales because he has a reputation as a potential gun-grabber.
Sales haven't gone up because there are lots of copycats planning their own missions, or because people are arming their kids; they've gone up because some people are hard at work attempting to strip others of their right to ownership.
Oh, and LaPierre is an idiot, lest someone think I'm taking his side.