breechblock vs blockage

breechblock and blockage both are nouns.

Word	Noun	Adjective	Verb	Adverb
breechblock	Yes	No	No	No
blockage	Yes	No	No	No

As nouns, blockage is a hypernym of breechblock; that is, blockage is a word with a broader meaning than breechblock:

breechblock: a metal block in breech-loading firearms that is withdrawn to insert a cartridge and replaced to close the breech before firing
blockage: an obstruction in a pipe or tube

Other hypernyms of breechblock include block, closure, occlusion, stop, stoppage.

breechblock (noun)	blockage (noun)
a metal block in breech-loading firearms that is withdrawn to insert a cartridge and replaced to close the breech before firing	the act of blocking
	an obstruction in a pipe or tube
	the physical condition of blocking or filling a passage with an obstruction