hired gun vs stickup man

hired gun

noun
  • A person who is employed as an armed guard, enforcer, or mercenary and who is prepared to use gunplay or similar violent methods in order to assert the interests of his or her employer. 

  • A person who is employed to advance the interests of his or her employer, especially in a vigorous manner using such methods as political lobbying, legal advocacy, or persuasion. 

stickup man

How often have the words hired gun and stickup man occurred in a corpus of books? (source: Google Ngram Viewer )