Vladof shotgun barrel

i am trying to use the faisor atm and i wonder if the shotgun barrel is considered a shotgun or still an AR, regarding weapon damage bonus

I would think AR since that what the card lists it as but that’s just a best guess.

Just use a relic that boost your damage of interest and test at the dummy with and w/o have it equipped.
Then it’s just a matter of shooting with the underbarrel.