Fugitives On The Run

When Rich checks the gun in the taxi, he first pulls the slide back with the magazine in the well. This not only reveals the chamber to be empty, but it would have loaded a round (and ejected a round had one been chambered, which an agent would almost certainly have been carrying with a round chambered). He then ejects the mag to check it, and you can see that there are no rounds in it. The mag also appears to be fake due to the design of the top portion.

References Star Wars: Episode IV - A New Hope (1977)