bust a cap vs pull the trigger

bust a cap

verb
  • To fire a weapon; to shoot with a gun. 

pull the trigger

verb
  • To fire a gun. 

  • To shoot, kick the ball in hope of scoring a goal. 

  • To commit to a course of action. 

  • To hit a very powerful shot. 

How often have the words bust a cap and pull the trigger occurred in a corpus of books? (source: Google Ngram Viewer )