The news of Independence USA PAC's big spending follows a report by Time magazine that said Bloomberg was considering whether to to start wading into the race. McAuliffe's Republican opponent, Attorney General Ken Cuccinelli, has taken a strong pro-gun rights position.
A number of other gun groups have already started spending in the final weeks of the race.
Independence USA PAC has previously hit political candidates on gun control. In February, the super PAC released an ad attacking two Democratic congressional candidates in the race for former Rep. Jesse Jackson Jr.'s (D-IL) congressional seat.