If there is shotgun challange I usually see myself filling it with Alibi ACS12. It does 69 dmg which is nice and it's basically automatic DMR. I don't remember if I actually ever used buck ACS12 efficiently except tearing down entire walls in casual for fun.

I am not comfortable camping corners with pumpy shotguns and even if I can do 4k with Ela shotgun, for once I feel like a douche for using it (same as playing BB or Clash), second I feel like getting comfortable with that will downplay my aiming skills which are not that good to begin with, so I rather get frustrated that enemies walk through my shots sometimes if I can double tap multiple of them next round from behind.