breechblock vs breech closer

breechblock and breech closer both are nouns.

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

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

breechblock and breech closer: a metal block in breech-loading firearms that is withdrawn to insert a cartridge and replaced to close the breech before firing

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a metal block in breech-loading firearms that is withdrawn to insert a cartridge and replaced to close the breech before firing	a metal block in breech-loading firearms that is withdrawn to insert a cartridge and replaced to close the breech before firing