Lyric discussion by LaniLuv49 

Cover art for Cannon lyrics by Self

I think the "cannon" referred to in this song is a metaphor for a person. Maybe it's a song about someone who is unaware of their own power (hence, a cannon) or has trouble controlling their temper ("when fire meets powder" may be when the person gets angry and turns into a loose cannon). Maybe the person writing the song is trying to tell this "cannon" that they're a burden by being "unessesary noise".