rear of tube vs breech

rear of tube and breech both are nouns.

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

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

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

Other synonyms of rear of tube include rear of barrel.

rear of tube (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