Tac-14 build with a bunch of damage, dmg resistance, accuracy and a bit of mobility. Hunker down allows you to have near perfect accuracy while crouched for long range and weakspots while keeping a wider spread while standing for crowds.
I haven't tested this on nightmare, strong and fun in veteran.
Character choice is Hoffman only because of his starting weapon. You may pick any character but you need rng to find a Tac-14 then.
Prefer Tec-9 as sidearm for crowds due to large mag size allowing to stunlock a large number of commons. No need for long range sidearm since when you get both accuracy cards you can snipe with the shotgun.
Shredder works per pellet so landing all pellets of a single shot makes the target take 12% more damage from all players.
Run like hell card sets your accuracy to 20% instead of reducing it by 20% so the accuracy cards do not negate the downside of run like hell. May want to consider fleet of foot as substitute.
You can crouch while jumping to get the accuracy from hunker down. This allows you to sprint jump to keep your momentum while firing accurate shots.
Buckshot bruiser is seen and might be underwhelming (and bugged, it can take health from you in a specific situation.) But it enables numb, helps negate damage even if it's not as crazy as with melee builds and it helps retain temp hp gained from pills.
Shell carrier and rolling thunder are very low impact here. These are the first to go out of the deck if you need something else added.