rear of barrel vs breech

rear of barrel and breech both are nouns.

Word	Noun	Adjective	Verb	Adverb
rear of barrel	Yes	No	No	No
breech	Yes	No	No	No

As nouns, rear of barrel and breech are synonyms defined as:

rear of barrel and breech: opening in the rear of the barrel of a gun where bullets can be loaded

Other synonyms of rear of barrel include rear of tube.

rear of barrel (noun)	breech (noun)
opening in the rear of the barrel of a gun where bullets can be loaded	opening in the rear of the barrel of a gun where bullets can be loaded