Which ship from Nukemod do you mean, and which box in PCS (pic)? The thread you referred to takes a very long time to load.
PC Rumrunner. The box I'm talking about is on the right of the screen -- the panel that shows various options, like to create, duplicate, or delete turrets, and so on.
Here's the ship's selected, showing a properties field. I would assume that is where the turret one is meant to be.https://imgur.com/It3zEEG
Here's a turret selected, with no properties field visible:https://imgur.com/AloziNG
As a further test, make sure that the turret has the fire down normals and fire on target flags enabled.
That may be it! I'll check.
EDIT: That's done it! Thanks!
Man, how'd you know? It's like you're psychic or something.
The impression I'm getting is that these models may either be half-finished or predate a lot of modern conventions. The turrets on the Rumrunner (and the Valhalla and Ragnarok) had no flags on them whatsoever.
Anyway. I'm not really any closer to understanding how PCS works, but the immediate problem is fixed, so that's good.