If you run into Hells arena at level 2, you will gain duel gunner after the first round/in the middle of second round if you killed everything in level 1 and 2.
It is completely possible to do, its not even that hard if you have enough ammo.
Just take down the souls and demons first, avoid the cacodemons and attempt to corner shoot them, if you don't have dual gunner yet, switch guns each time you run out before reloading.
Barons aren't that diffucult with Dual Gunner if you keep your distance.