You need to learn to quick LT with the Gnasher at first, the hipfire shotgun is pretty simple, just judge the middle of screen but if your hit use the damage circle as aiming aid. You need to learn to be quick with your movement and decision making. Make sure you use cover correctly, you gotta learn to wall bounce at the correct times too. Also when in shotgun battles learn to strafe as i said before movement is everything in this game. There is little tricks to learn too like the fake wallbounce. Always try and get the right angle on your opponent when in cover battles or moving around objects having the left angle is a disadvantage. The real power weapon on this game is the Lancer, so strong and the stopping power is strong as hell. I play competitive so only use a Gnasher Lancer Set up. But from what ive played in ranked rooms the Retro is really powerful mid-close range, the hammerburst is strong too. The sawn off is cheap but you won't be clutching any 2 vs 1's as Close Quarters with it. If ya want add me my GT is True kiliah , i'll play along and can also join our private King of the Hill rooms which we just use for shotty practice.