hang fire vs maintain

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. 

maintain

verb
  • To keep up; to preserve; to uphold (a state, condition etc.). 

  • To declare or affirm (a clause) to be true; to assert. 

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