Right, I'm bitter about this now- partly because those of you that do use GB turrets on trains seem totally nonchalant about it and partly because I just wrote like 5 paragraphs on the subject, forgot my internet at work logs out automatically and proceeded to erase everything I'd just written. So I'll get to the point faster this time and probably sound a bit more abrasive than my normal cheery self:
This is the same as the Mars Flyer turrets issue, it's not that these weapons are massively more powerful/accurate/whatever, it's that players go out of their way to exploit these holes in Discovery that annoys me.
I would prefer that trains and civilian freighter-craft be half as strong as they are now. There are enough trains on the server at pretty much any time to create a convoy for safety, and it would also open up the market for meaningful escorts. The way it is, any rogue trader can fly the whole of Sirius untroubled, and that severely detracts from roleplay (which is not a good thing any way you look at it).
Funny that mostly veteran Discovery players here agree with me, yet the newer ones do not.