hang fire vs hold one's horses

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 one's horses

verb

  • To be patient; to wait. 

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