a gat in the hand means a world by the tail

ChandlerのThe Big Sleep を読んでいます。
I reached for it. Brody took a gun out of the cigar box and pointed it at my nose. I looked at the gun. It was a black Police .39. I had no argument against it at the moment.
Neat, huh? Brody said. Just kind of stand up a minute. Come forward just about two yards. You might grab a little air while you're doing that. His voice was the elaborately casual voice of the tough guy in pictures. Pictures have made them all like that.
Tsk, tsk, I said, not moving at all. Such a lot of guns around town and so few brains. You're the second guy I've met within hours who seems to think a gat in the hand means a world by the tail. Put it down and don't be silly, Joe.
"gat in the hand means a world by the tail" の "a world by the tail" はMary Higgins Clarkの "Before I Say Good-Bye" を読んだ時に出てきた "get the world by the tail"(3/27/2017") の意味ですね。
今日調べるのは "gat" の意味です。
・Oxford English Dictionary: A revolver or pistol.: Teenagers with gats chased all her guests away.
・Wiktionary: a. (archaic, slang, in old westerns) A Gatling gun. b. (1920s gangster slang) Any type of gun, usually a pistol.
Origin: From Gatling gun, after inventor Richard Gatling.
西部劇あるいはChandler作品の様な古い探偵物にしか出てこなそうな単語でした。