Unfortunately it is the perfect storm.
UN Small Arms Treaty, Presidential Election and the Dec. 21 Mayan Stuff.
People are getting concerned/paranoid depending on thier view.
Now add in the almost constant bombardment of "doomsday" shows on TV (Doomsday Preppers, Doomsday Bunkers, Falling Skies, Walking Dead, new show called Revolution (I think?) about emp/sun flare). Heck I even see a good amount of .gov sponsered preparedness commercials. The society is being saturated with this stuff.
As most mentioned, the run already started back before new years. XM855 has already gone up 25% in the last couple of months. Was going for around $400/k and last I saw in the latest uber goober CTD catalog was around $500/940ish rounds.
Likewise, I do anticpate new high level taxes being imposed on ammunition, etc.