3/15/2011 8:00 AM PDT
Talk about going ballistic ... TMZ has learned the guys from "Pawn Stars" have purchased a guidance system for a missile often used on F-4 Phantom fighter planes!!!

Sources connected to the deal tell us Rick Harrison and his team made the deal for an AIM-120 AMRAAM missile last week ... along with the "front part" of the missile.

And before you freak out -- we're told the "front part" of the missile did NOT contain a live war head ... obviously.

Our source could not confirm how much cash Rick shelled out for the parts ... but we're guessing they don't come cheap.

So far, no word on the identity of the person who was running around Las Vegas with pieces to a missile ... but we're told the deal was "100% legal."