Autoguns are a very enjoyable grouping of guns to use in Darktide, from the quick sprays of the the autopistol to the clean headshots of the Vraks VII headhunter (The semi automatic DMR styled headhunter) but there are a few major issues with them.
The first major issue is ammo capacity, both of the magazines and in the player’s pockets throughout a round. my current agripinaa infantry autogun holds 27 shots in a magazine with a meager 305 rounds as a sharpshooter. It becomes excessive to the point of having to hog the ammo tin, stashes and crates just to perform my main role. Ranged special and elite killing. On other classes, even with higher tier autoguns and pistols, the ammo reserves become a problem that tends to neuter their ability to perform in ranged engagements like the long hallways that lead into doorways which are very common and almost always have little to no usable cover.
Second, the wonky choice to have hip spraying as the choice for the autopistol and braced autoguns. As it stands, it is a worse idea to brace the autopistol as it widens the reticle while just firing the weapon makes it moderately successful in an engagement inside a small to medium sized room with about 5-10 meters of distance between you and a target. The braced autoguns are just awkward to brace, the reticle does not accurately display how the bullets will move and the autoaiming system is just awkward with little to no control on who it targets and how many shots will be used to kill a target.
Finally, there is little reason in any difficulty above malice to use the autoguns when the lasrifles will do every part better. You want incredibly powerful killing potential in a more backline role, you choose the Lucius pattern Lasgun or the Kantrael MG XII lasgun. You want good close quarters engagement potential, you choose the Accatran patterns or the Kantrael MG Ia or IV lasgun.
Now for my suggestions as to fixing these problems. Buffing the carrying capacity of the autoguns by a 25 - 30% to bring it more in line with the carrying capacities of the laser weapons. Especially with the high firerates present, this allows for a stronger ammo economy and helps to slow the ammo consumption that would help to keep a zealot with a flamer or bolter firing for longer. Second, give the autopistol and the braced autoguns an actual ADS, allow them to flourish in longer ranges than right in front of the player which will also help them succeed in more suppresive roles as well, laying down a lot of fire to keep a squad of scabs pinned as a zealot closes in for the kill or a psyker gets that little bit more time to brain burst a gunner. Finally, an option for a scope on all of them, with the exception of the autopistol (and scopes for most long arms as well) would do wonders in helping with their performance in longer ranges and rooms with large sightlines like the position you hold to open the massive door in the consignment yard raid mission.
An idea that could further help to differentiate the two and offer a more nuanced choice between energy weapons and ballistic weapons could be varying performance between the two against armors and flesh. This would require some retooling of systems and to make it more meaningful the ability to know what group you will be primarily fighting, Dreg or Scab.