Disclaimer: I have literally only just bought the core rulebook, but the consensus on the boards seems to be that bolters in general and heavy bolters in particular are too damned good.
Most of the fixes I've seen proposed basically boil down to nerfing their damage, but this strikes me as missing the central problem.
Near as I can figure it, the problem with bolters isn't so much the fact that they have high base damage (after all, an average punch from a Space Marine does pretty hefty damage) as that thanks to semi- and full-auto fire, the damage from repeat-firing weapons scales with Ballistic Skill when damage from other sorts of weapons doesn't. Even with armour and toughness reducing each hit independently, ten Heavy Bolter rounds doing 2D10 + 10 damage are going to be more effective against a single large target than a 6D10 + 10 Lascannon, particularly when Righteous Fury is taken into account.
The more I think about it, the more I think this problem comes from the fact that automatic fire allows for multiple hits against a single target in a single round, and in order for one shot to do a respectable amount of damage, a full-auto burst has to be able to do a completely *insane* amount of damage, because the amount of damage has to scale linearly with the number of shots fired. This has the counter-intuitive effect of making the best weapons for dealing heavy single-target damage the weapons designed for clearing out waves of infantry.
As a result, my proposed fix to the system (on the basis of no playtesting, but having used Heavy Weapons in Dark Heresy) is this:
When firing a weapon on semi- or full-auto, each hit after the first loses 1D10 damage, cumulatively, until no dice are rolled.
So one Heavy Bolter hit would deal 2D10 + 10 damage, the second hit against the same target would deal 1D10 + 10, the next just 10.
This seems initially counter-intuitive (logically three bullets should hurt three times as much as one bullet) but remember that damage is abstract, and it isn't immediately obvious why the amount of game-mechanical damage from the second bullet should be the same as the damage from the first (indeed when one is firing at a large, heavily armoured target it seems unreasonable that *all* of the bullets striking the target should hit vulnerable spots - which is what a hit for full damage would seem to imply) .
The advantage of this suggestion (and apologies if it has been suggested and/or shot down before) is that it seems to be a way to control the Heavy Bolter as a single-target weapon, without compromising its effectiveness in its setting-appropriate niche. It leaves the Heavy Bolter as your weapon of choice against Elites while making higher damage-per-hit weapons more effective against large, heavily armoured enemies.
Or maybe I'm talking complete nonsense. Thoughts?