For things like the AT rifle and LMGs, it should be harder to turn on a dime. The common solution to this is to decrease turning speed or sensitivity, but this doesn't work because people can just turn up their mouse sensitivity in the menu or in their OS.
Instead, I propose that heavy weapons being carried at the hip should have inertia: the faster you turn with a heavy weapon, the more it will want to keep moving in that direction unless you pull back on it. Metro 2033 had a good example of this. In the following video (where this dumb guy keeps swearing), you are piggybacking a child back to his home station while you fight off mutants. Having the kid on your back changes your centre of gravity, so turning your body (your view) makes your view continue towards the direction you were turning, and to stop it quickly you need to pull your weight back in the opposite direction to compensate. Small, controlled movements are less susceptible to this drift.
Let's Play: Metro 2033 - Episode 24: Piggyback Ride - YouTube
Aiming should be as normal when deployed or when using a different weapon, though. This would further encourage deployed firing, while making hipfire more challenging (but still possible).
Instead, I propose that heavy weapons being carried at the hip should have inertia: the faster you turn with a heavy weapon, the more it will want to keep moving in that direction unless you pull back on it. Metro 2033 had a good example of this. In the following video (where this dumb guy keeps swearing), you are piggybacking a child back to his home station while you fight off mutants. Having the kid on your back changes your centre of gravity, so turning your body (your view) makes your view continue towards the direction you were turning, and to stop it quickly you need to pull your weight back in the opposite direction to compensate. Small, controlled movements are less susceptible to this drift.
Skip to 6:30 for the piggyback sequence.
Let's Play: Metro 2033 - Episode 24: Piggyback Ride - YouTube
Aiming should be as normal when deployed or when using a different weapon, though. This would further encourage deployed firing, while making hipfire more challenging (but still possible).