Because the town sheriff, Andy Taylor (Andy Griffith) wouldn't trust Barney with a loaded gun, for fear of accidentally shooting himself or an innocent bystander, Barney never carried a loaded gun, but rather kept one bullet in his left shirt breast pocket.

The only time he used his gun was to start the potato sack races for the annual Mason's picnic.

Barney Fife's Revolver

Barney was jokingly called Barney the Beast, Barney the Fierce, Crazy Gun Barney and Fearless Fife by his fellow townsfolk's.

On episode No. 9 "Andy, the Matchmaker" someone in town wrote the following limerick on the side of the Mayberry bank:

"There once was a deputy called Fife, Who carried a gun and a knife. The gun was all dusty, And his knife was all rusty, Because he never caught a crook in his life."

See also - "The Sheriff Without A Gun