percussion cap vs priming

percussion cap

noun
  • a metal cap found on muzzleloading firearms that contains chemical substances such as fulminate that explode upon impact 

priming

noun
  • The powder or other combustible used to communicate fire to a charge of gunpowder, as in a firearm. 

  • The implicit memory effect in which exposure to a stimulus influences response to a subsequent stimulus. 

  • The carrying over of water, with the steam, from the boiler, as into the cylinder. 

  • A substance used as a primer. 

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