MX vs ammunition

MX

noun
  • on early British stamps, Maltese Cross cancellation mark. 

ammunition

verb
  • To supply with ammunition. 

noun
  • Articles used in charging firearms and ordnance of all kinds; as powder, balls, shot, shells, percussion caps, rockets, etc. 

  • Arguments and information that can be used against the other party in a conflict. 

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