rapid-fire gun; quick-fire gun
Refers to a weapon capable of firing rapidly, such as a machine gun or autocannon. The term is somewhat technical and not an everyday word.
This tank is equipped with a powerful rapid-fire gun.
talking rapidly; barrage of words
Colloquial metaphorical use, likening fast, continuous speech to rapid gunfire. Often used in phrases like 速射砲のような質問 (a rapid-fire barrage of questions).
He kept talking like a rapid-fire gun.
A barrage of questions flew from the reporters.
Compound of 速射 (rapid fire) and 砲 (gun, cannon). The colloquial sense is a metaphorical extension of the rapid, continuous nature of gunfire to speech.