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Phrase(s): beat the gun
Fig. to manage to do something before the ending signal. (Originally from sports, referring to scoring in the last seconds of a game just before the referee fires a gun to signal the end of the game.) • The field goal beat the gun and was in the air just in time. • Tom tried to beat the gun, but he was one second too slow.
McGrawhill's American Idioms And Phrasal Verbs