i dont understand heavy bolter

Just finished maxing out my first class (vanguard) so I decided to go back to playing some of my less-used classes. I had a nice time playing heavy plasma and multi-melta, and got both to relic without any trouble, but heavy bolter... oh man. I dunno. I can't figure it out. Yesterday I was easily running through absolute on vanguard, and now i'm getting wiped on substantial decapitation with heavy bolter.

It just feels so... clunky. Heavy stance seems like the only viable way to use the weapon (accuracy sucks so bad otherwise) but ducking in and out of heavy stance while trying to dodge and stuff does NOT feel good. The damage is NOT great either. I've only gotten it to green so far but it hasn't been enjoyable at all.

Am I missing something? Am I just playing it completely wrong?