Emilio Estevez's Gun and Ammo Stolen During Car Break-In

Emilio Estevez is way past playing Billy the Kid ... especially now that cops tell us his gun was stolen.

Law enforcement sources say the incident went down back in May as the 'Mighty Ducks' and "Young Guns" star was staying at the Oceana hotel in Santa Monica.

We're told he parked his car with the valet ...and 2 days later got back in his car only to find his Glock and ammo were missing. Our sources say there was no forced entry. It's unclear where the gun and ammo were in the car.

Cops are investigating.