NPCs in fallout shelter with larger weapons(mini guns,rocket launchers, ect) run back and forth in between rooms and do not attack raiders or rad oracles

They will only fight in the rooms they are assigned to. They will not follow raiders or roaches out of their assigned rooms. If the dweller is pregnant they will not fight no matter how well they are armed, instead they will run out of the room to protect the baby. If they are on coffee break and wander into a room where combat is going on, they will run around and then leave the room.

You can temporarily assign a dweller to a room during an incident but if that room is already full, they will swap places with a dweller in that room, after the incident is over, all dwellers will return to the rooms (or coffee break) that they were in when the incident started.

As an example: You have a beginning vault with all the rooms on the first level so it would look like, Vault Door, Elevator, Living Quarters, Power Generator, Diner, Water Treatment.

You have two dwellers on coffee break wandering around the first floor (basically) travelling back and forth between the Vault Door and the Water Treatment rooms. They are both armed with a lever actions and they have 2's in all their SPECIAL attributes.

You have two dwellers assigned to the Power room. One with a strength of 2 and armed with a minigun and one with a strength of 4 armed with a 10mm pistol.

You have two dwellers assigned to the Diner. One with an Agility of 2 and armed with a lever action and one with an Agility of 4 armed with a .32 cal pistol.

You have one dweller assigned to Water with a Perception of 5 and a minigun.

Raiders attack. While they are beating on the vault door, you drag both of your coffee break dwellers to the vault door room. This gives them a temporary assignment there and they will defend it. If they kill the raiders, the incident will be over and they will return to coffee break. BUT...

After a while if the raiders are not killed, they will move to the next room to the right (Living Quarters). The two dwellers you put in the vault door room will NOT follow them. You have to drag those to into the Living Quarters (another temporary assignment). After a while, if the raiders are not killed, they will move to the next room to the right (Power Generator). Again, our two heroes will not follow them.

The raiders will start fighting your Power Generator dwellers. The room is full so if you try to move one of the coffee break individuals into the the room to help, he will switch places with the lowest strength person in the room (the one with the minigun). So now the power generator dweller with the minigun is temporarily assigned to the Living Quarters.

After the raiders have been in your Power Generator for a while, they will move to the Diner. Again nobody will follow them. The Diner is also full so anyone you move in there to help, will wind up replacing the person in their with the lowest Agility.

After the raiders have spent a little time in your Diner, they will move one room to the right again and wind up in your Water Treatment room. Again, nobody will follow them. Water Treatment only has one dweller assigned to it, so if you move the Power Generator dweller with the minigun (who has been temporarily assigned to the Living Quarters), that dweller will not replace anyone. But if you try to move another dweller in there, the room now is temporarily full so it will replace the lowest Perception individual (and in this case that would probably be the dweller with the minigun you just moved in there).

As you can see. If you try to help out too much, you can have a lot of people running around not really doing anything because while your dwellers are moving, they are not doing anything else.

Perhaps you've misunderstood the nature of this bug? I've experienced it as well, and seen other threads about it.

The "first" room in my Vault is a Power Plant, there are 6 Dwellers assigned here, with my best weapons. One of those weapons is Vengeance. When Raiders attack, or Radroaches appear, Willie Miller gets Vengeance out and proceeds to run back and forth across the room, never firing.

On the level below, another Dweller has a Rusty Flamethrower. During a Radraoch attack, I noticed her doing the same thing.

These dwellers are not moving because I instructed them to. At the beginning of an incident, and periodically during the incident, dwellers in combat will reposition themselves before firing; it appears that dwellers with heavy weapons get stuck in an endless loop of repositioning themselves, and never get around to actually using their weapons.

y, I can acknowledge this bug exists. If you put two dwellers armed with gatling lasers in the vault room, they just run back and forth when raiders attack. It's as if they are trying to get range to fire the gun. I have just got a hardened mini gun and put this in the vault room with a gatling laser armed dweller and it works ok.

I don't think it matters, since they'll do their damage anyway.

I think damage from all dwellers' weapons in the room is just added up and then applied to a raider, doing damage over time, so the animations are probably just for show. Often enough I see raiders die while my dwellers aren't even firing at that moment.

Agreed. The animation is irrelevant to the mechanics under the hood. Sometimes the animation won't show a single shot fired, but The Enemy winds up just as dead.

I considered the possibility that it was just the animation (and not the damage) that was faulty, but when I raised the issue with support I was referred to the forums. Confirmation either way would be well received.

How nice of them, considering they do precious little actual support on here!

Respect for posing such a long and detailed explanation.

Well since the mechanics seem to work fine, I guess it can't really be considered a bug.

Yea, but it wasn't relevant to OP's issue. Read GhostWolfe's reply.