I've never played Rogue Trader before, but I'm readfing the rules and making characters just for run. If I ever do get to play it I'd probably be the one GMing. Some questions:

Hypothetically let's say I have an Explorator (assuming sufficient XP to get to the various Ranks and Talents, etc) who has a Good quality MIU, MIU weapon interface, MIU-controlled Plasma Gun mounted to his shoulder, other Plasma Gun in hand, and Plasma Pistol mounted to a Ballistic Mechadendrite (has Machinatior Array to allow this).

1. If the Plasma Gun he's carrying in his hands (the old fashioned way) is of "Good" quality, does this affect the Overheating in any way? In the rules it says that Overheating weapons never jam, and if they would ever be forced to jam, count it as an overheat instead. "Good" quality guns are supposed to be Reliable, which might lead you to make the inference that in the case of Overheating guns, the "Reliable" trait as gained by a Good quality Plasma Gun would apply to the Overheating, i.e. when it overheats you roll a d10 and it only overheats on a 10, for example. I don't see any mention of this in the rules, so by the strict interpretation of what I've read, the Good quality as applied to a Plasma Gun would do basically nothing and would not affect the Overheating at all, but I wondered if there's a clarification I'm not seeing or a popular house rule about this.

2. When the shoulder-mounted MIU-linked Plasma Gun overheats, does the Explorator take damage as normal (as if he were holding it in his hands)? Does he still have the option of dropping the MIU-mounted gun as a free action (as a GM I would rule "No." to that)? If he does take damage as normal, does his armor soak up any of it, or does the shoulder mounting of the gun cause the damage to go straight to the Explorator, bypassing the armor entirely?

3. When the Plasma Pistol on the Ballistic Mechadendrite overheats, does the Explorator take damage? Can he drop the pistol to avoide this? Does his armor help him at all?

4. The MIU-mouted weapon can apparently fire as a free action in addition whatever else the Explorator is doing, which I take to mean he can fire the gun he's carrying in his hands and also fire the MIU gun in the same turn. Is that right?

5. The Mechadendrite-mounted Pistol can fire as a Reaction or as a Half Action Attack during his turn. If it fires as a Half Action Attack during the turn, I assume that that shot is then the ONE Attack action he can take that turn, so basically the only way to gain another shot per round is to use the Mechadendrite-mounted pistol as a Reaction during someone else's turn, right?

Edit:

6. Some cybernetic implants have no listed quality levels. If I get a free "Poor" quality cybernetic part via the Criminal background ("Judged and Found Wanting") can I take one of these implants at "Poor" quality even though no quaity level exist for it? If so does the "Poor" quality have any effect on the cybernetic? The MIU Weapon Interface is one such item, so in the above example, from what I've read, it would seem like the Explorator could get that implant as a free item upon creation, at poor quality, but that Poorness would not have any adverse effect on his Ballistic Skill for shots with that weapon, is that right?

7. Assuming the weight isn't a problem (Suspensors?) can a Heavy Weapon like a Multi-Melta, Rocket Launcher, Plasma Cannon, etc be mouinted to the MIU on the shoulder?

8. When a gun connected to a large ammo supply (i.e. a Heavy gun) jams, do you lose all of the ammo in the big ammo supply just as if you had a jam with a regular-sized normal magazine?

Any additional clarity you can give me on any of this would be appreciated, including if the above character as constructed is not legally possible in any way. Thanks in advance for your help.

1. On Good-craftsmanship/Reliable vs. Overheat

• I rule that Jam and Overheat are equivalent results; if a weapon is prevented from Jamming, it's also prevented from Overheating.

2. On a Shoulder-mounted Weapon's Overheat

• Dropping it is not an option, no. The character soaks the weapon's 0 Pen Damage normally. However, the hit location is up in the air. I would say it's either a Head or a Body hit, based on the weapon's proximity to those areas.

3. On a Mechadendrite-mounted Weapon's Overheat

• I'm not sure how I would treat this one. Gut instinct is to either disable the mechadendrite temporarily or knock its quality down one level. Maybe someone else will have a more definitive answer for you.

4. On the Number of Attacks the Explorator can Make

• The Explorator can make one Attack-subtype action per Turn, as per the Errata; the Explorator can attack with his limbs normally or as a Free Action with the MIU, but not both.

5. On the Ballistic Mechadendrite

• On the Explorator's Turn, he can attack with the mechadendrite as a Half Action. On anyone else's Turn, he can attack with the mechadendrite as a Reaction. So yes, the only way to generate more than one shot per Round is to use a Reaction on someone else's Turn.

6. On Poor-craftsmanship Cybernetics

• Any Poor-craftsmanship cybernetic is going to negatively influence the normal effect of the item. For the MIU-WI, I would say it can't receive bonuses to BS, completely breaks on rolled doubles, or something. For "Judged and Found Wanting", I would say MIU-WI is simply not a valid choice. Personally, I think it's supposed to mean something simple like an arm or an eye, not something extravagant and unnecessary for daily life.

7. On Heavy Shoulder Weapons

• Going by the Errata and common sense, the Basic weapons are largest weapons that should be shoulder-mounted. That being said, an MIU-WI'd weapon doesn't have to be shoulder-mounted. It could be a weapon that's part of a vehicle or other structure.

8. On Large Ammo Jams

• I don't have any experience regarding Jams, but I also don't think it's quite right voiding an entire clip to resolve a Jam. Someone else can offer a more substantial answer than I can.

I'll be around if you want a follow-up.

Thanks for the respnse. In the Errata (I JUST NOW read the Q and A section, after reading your response, duh!) it says that the MIU shoulder mount should not go above Pistol sized weapons, and that although it makes shooting said pistol weapon a free action, that does not grant any additional attacks.

The pistol size restriction is, I think, a house-rule-able thing. As GM I would let people go up to Basic size, but I would probaby reastrict the firing arc. A shoulder mounted pistol that's on the right shoulder could probably fire in a 270 deg arc that excludes the leftmost 90 deg (you can't fire across your own neck!) whereas I might restrict the larger, and more awkward Basic size weapons to only the front 90 deg, which would make a difference if the Explorator is working on something and trying to shoot at people sneaking up behind him, for example. I might also hit the Ballistic Skill test with a -10 for the Basic gun.

As for the "no additional attacks" rule stated in the Errata, this is, in my opinion, in direct contradiction to the way the MIU Weapon Interface description is worded, as it reads "This system allows user to fire an additional ranged weapon as a Free Action—using his full Ballistic Skill—no matter what other actions he may be taking at the time." I don't see how any rational person could have read that and NOT come to the conclusion of "So I get a second shooting attack in the same round when I shoot my OTHER gun, sweet!" I think this errata was written so as to nerf what would otherwise have been a "too powerful" item in the book as written, and I agree that it's probably too powerful if you get two shooting attacks in the same round with just 2 cybernetics that are available at creation. That said, a person with two pistols and the right Talents can fire both of those as a single shooting action, so this would not have been entirely unprecedented. This is an example of altering the rules substantially via the Errata not simply clarifying them, in my opinion. I frown on that because it get's the player's hopes up then dashes them in the fine print, but I accept it for the sake of the other classes not getting totally outclassed by the Explorator at square one of character creation.