Can you mount a Heavy weapon on a MIU Weapon Interface? I can't see anything saying that you can't do that. I would guess that you must brace the weapon before firing as usual. This brings up the very cool mental image of a Tech-priest planting his legs in a wide stance while his shoulder-mounted minigun locks into place and begins spinning with a high-pitched whine...

Can an MIU-Interfaced weapon be used as part of a Two-weapon Wielder attack? RAW it seems as though this is not possible. This is probably for balance reasons, as dual-wielding heavy weapons would be obscenely busted.

The text of the MIU Weapon Interface says that the interfaced weapon may be fired as a Free Action. What happens if I want to make a Called Shot or Suppressing Fire attack (both Full Actions) with an MIU weapon? I can imagine close combat specialist types wanting to supress their enemies while closing into melee range, but the MIU is unclear about how this works.

Without looking at the text , I imagine the model for firing it was how mechadendrites work.

Which makes me wonder why the thing even exists, since it does exactly the same thing as a ballistic mechandendrite.

I do not believe you can carry and fire a 40-kilogram gun on one shoulder with no other support, cybernetic implants or no cybernetic implants.

Hmm... I haven't read the rules on this completely, so I'm confused.

A MIU is a Mind Interface Unit. In the original 40k book it was described as Bluetooth technology but run by the inherent but latent psychic potential all humans (except Nulls) possess. Pretty impressive, seeing as Bluetooth was still 15-20 years away at the time 40k was written.

MIU's were mainly used for remote controlling things. Servitors, cyber-skulls, mechadendrites and enhancing your weapon's ability to score hits. It also hinted that there were limits to the number of objects you could control with MIU's, that there were better qualities (more objects could be controlled) and that installed MIU's had to be linked to specific objects and had to be re-programmed to access different objects. For instance, an MIU controlling a cyber-skull would have to be reprogrammed to interface with a Servitor.

There's been a lot of debate over the years on what an MIU consists of and how they work, but speaking from a strictly old-school 40k perspective, an MIU weapon interface would not allow you to fire the weapon as a free action unless the weapon was installed in a mechadendrite. OR a shoulder-mounted weapon. There used to be a big difference. Are shoulder-mounted weapons considered mechadendrites now?

While you could put an MIU Weapon Interface on a Heavy Bolter, it would give you different benefits.

Long, long ago in an Imperium far, far away, a normal dude (guardsman, noble, Space Marine) could have an MIU implanted in his skull and link it to the appropriate hardware mounted on his gun which gave him bonuses to hit with it. I think you could also use it as a camera, i.e. point it around a corner.