breech closer vs breechblock

breech closer and breechblock both are nouns.

Word	Noun	Adjective	Verb	Adverb
breech closer	Yes	No	No	No
breechblock	Yes	No	No	No

As nouns, breech closer and breechblock are synonyms defined as:

breech closer and breechblock: a metal block in breech-loading firearms that is withdrawn to insert a cartridge and replaced to close the breech before firing

breech closer (noun)	breechblock (noun)
a metal block in breech-loading firearms that is withdrawn to insert a cartridge and replaced to close the breech before firing	a metal block in breech-loading firearms that is withdrawn to insert a cartridge and replaced to close the breech before firing