I like to experiment myself.
I Kamakazee and gifted in one game, went melee and I was like OK! lets hide let the other members die first
But seriously I think if you tag small guns, big guns, and some utility skill like Steal, Traps, doctor. You should be good. Rocketlauncher is like a must ASAP because with high perception and fast shot trait youll be a unstoppable mofo. I know I sniped a few times with a rocket launcher and it was hilarious watching Mutants explode

.
However in my current game I tagged gifted and fast shot, then tag small guns and energy weapons and I was unstoppable *Cheated to get my bigguns up* but the point is that having small guns proves to be the bomb till you get energy weapons.
Tho atm im using a browning and leaving my party at the LZ

, and then run around sniping with the browning lol.
But the shotgun is GREAT! to snipe with

. TRUST ME!!!, single shot use it to snipe with a range of 30+ with good skill and right stats, you can kill 1 or 2 mutants together in 1 or 2 shots. Or if there in a line Burst mode and take out 5 mutants or reavers

. Done it before too, funny how it turned out

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But the Shotgun is the best weapon till energy weapons.