@rihanna SHOOTING UP Sin City

Rihanna did her best impression of Rambo Thursday night — when the singer let loose with some FULLY AUTOMATIC MACHINE GUNS … and OFFTOP has the crazy footage.

RiRi rolled up to the Guns and Ammo Garage in Las Vegas for a midnight session at the gun range — where we’re told she shot a variety of fully automatic weapons, including the SAW machine gun and the M4 and AR-15 rifles.

You gotta check out the video … because who doesn’t love watching a hot chick shoot a gun???

God bless America.

r