hang fire vs hold back

hang fire

verb
  • To wait or hold back. 

  • To fail to fire immediately when the trigger is pulled. 

noun
  • The situation when a gun does not immediately fire when the trigger is pulled, but may fire shortly after. 

hold back

verb
  • To contain; stop. 

  • To act with reserve; to contain one's full measure or power. 

  • To delay the progress of, especially in school. 

How often have the words hang fire and hold back occurred in a corpus of books? (source: Google Ngram Viewer )