MX vs projectile

MX

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

projectile

adj
  • Projecting or impelling forward. 

  • Caused or imparted by impulse or projection; impelled forward. 

noun
  • an object intended to be or having been fired from a weapon. 

  • any object propelled through space by the application of a force. 

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