battlefront vs firing line

battlefront

noun
  • The region or line along which opposing armies engage in combat. 

  • The area in which opponents or opposing ideas meet. 

firing line

noun
  • The line from which soldiers fire their weapons at a target; especially the front line of troops in a battle. 

  • The vanguard of an activity. 

  • A situation in which someone or something is targeted. 

  • A row of shooters. 

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