It isn't too complicated. The start: Obama became president.
All Republican media and talking heads: "Obama is coming for your ammo"
Every scared little conspiracy believer ran out and stocked up, causing regular shooters to stock up, causing casual shooters to stock up. Look at gun manufacturer and ammo manufacturers' stock prices while Obama was president. There's your "research". Simple, predictable paranoia. It will happen again when a Democrat becomes President again, the fear is real.
I have already stated that the public did not start the problem, that it came from something else. Yes, after it happened the public started buying everything out there. They did not create the problem to start with.