While fun to use, the shotguns currently in Darktide are underwhelming at best - which is too bad, as they’re really quite nice looking.
The Double Barrel simply needs more power. If it stays in its current form, it isn’t that much different from the other shotguns except in style. I’m not advising to change its spread, but one option would be to give it a much wider spread but more damage that drops off quickly, so that it can clear out all the chaff in a wide cone in front of you but is much less useful at longer ranges.
The other shotguns are poorly-defined (especially since the icons in-game don’t even make clear what special round they have; I can only remember each variety by their magazine sizes), and I think the simplest implementation would be to change their special ammo to being their default firing mode. A slug-firing shotgun, a shotgun that shoots dragon’s breath rounds, and a “normal” shotgun would seem quite fine, with some number tweaking. In general, they feel very weak, and there is a wider problem of inconsistency that plagues all the shotguns. I’ll come back to that. If their special fire modes became default, they could get a melee bash, or they could just get flashlights. Or bayonets.
For the original three, a new blessing that lets you load two shells at a time would be a nice quality of life improvement. It’s a real technique, and would help cut down on the very long reloads at the cost of a blessing slot. It might be far from optimal (though you could always throw some other buff like narrowing hipfire spread on there) but I’d still consider running it, personally.
Coming back to the inconsistency; while that’s something that is inherent to a spread weapon, in a game it feels bad when you unload multiple rounds into a mid-tier enemy twenty feet away and they get back up. The minimum pellet count idea helps mitigate this, but you could also just do a line trace from the barrel and load a portion of the damage into that, so things directly under your sites take a predictably large chunk of damage. Just a thought.
Finally, it may be just me, but it has never made sense that shotguns are so bad against monsters. They’re typically used for hunting, and all those pellets would tear up a lot of surface on something big it hits. It just feels thematic to take a shotgun to go hunting big beasties.