Just finished Privateer Righteous Fire.

Does anyone know if you can actually recover your Steltek gun and remount it onto your ship?

I attacked Mordecai Jones last in the off chance that I could use a tractor beam to recover the gun and even made sure to draw him away from the asteroid field. I returned to the Retro temple. I jumped through the hidden nav point. I even went back to the Church of Man informant. He promised to destroy the Steltek plans but never returned the gun. You can just go back to Perry to claim your 80k reward. It seemed a bit anticlimactic to not recover it.

I don't think so. I played through the game maybe 4 or 5 times and never was able to recover the Steltek gun after the start of Righteous Fire. What you can do is find one secret jump point somewhere in a system close to New Constantinople, but not the one up in Farriss to the new system.

You don't really need, though. The four Fusion Cannon Centurion is a beast. With the Orion in RF two Plasma Guns are very fitting. And for the Galaxy - well, I tend to use the Tachyons for that one (as for the Tarsus- but before that you'd have to play through Privateer in a Tarsus which is a tough nut).

Here is some interesting information on the weapons in Privateer:
http://apocalyptech.com/linux/privgun/
Another site with much info I strongly recommend:
http://www.classicgaming.cc/pc/privateer/

It is indeed impossible...
btw. after cafeful examination of RF cutscenes, I am pretty much convinced, that Origin had planned another expansion for Privateer, which would have completed the plot - but for various reasons, that expansion never saw the light of the day (after all, Privateer itself is full of cut content, so nothing really new here...).

The Steltek gun has been nerfed in RF it is so weak you don't really want it back