About the only way would be to make your weapon mounted on the ship, when you purchase the ship.
You'd need to use a unique hardpoint name, but don't assign it anything in shiparch.ini
Only assign your weapon to that specific hardpoint in the ship's package in goods.ini
(Kinda like shields, runninglights, etcetera, are.)

And don't place it in the Market_Misc.ini file, or it could be repurchased, and placed on any suitable mount.

You could still sell the weapon, but once sold, it couldn't be repurchased.
(Even if it was, it couldn't be mounted to that hardpoint.)

(I've never tried it, so I'm not sure it'll work, but I think it will.)

As to your equipment question:
If it's on the ship, it's equippable, period.


Watch your 6!

There is another way. If you change any class 1 weapons to be class 2 instead (as no ships in the game can only mount class 1 guns), then give your specialist weapon that Hp type it would work ok. You would need to remove the:
hp_type = hp_gun_special_1, HpWeapon01.. from the shiparch of the other ships if you didn't want that weapon being mounted elsewhere.
It should work ok.

Thanks for the ideas, guys.

Yes, I got the part about having the weapon come stock and then not being able to equip it... I originally wanted people to have the option to add the weapon to the ship or not based on preference. Changing all other ships in the game would be a good way of doing it, except that it would interfere with other mods people wish to run... and considering that it's a stand-alone ship, I don't want to have to take modularity away. I figure that in the end I can just leave it as-is and forget about it, as really this is just covering up for people doing stupid things (like putting vanilla-FL turrets on floating hardpoints).

And on the equippable topic, I meant on the "Commodities" screen when you're actually flying in space, not the Equipment Dealer on a planet or station. You know, like how you can jettison nanobots and extra weapons you've picked up and stuff. What I wanted to know is if there was a way to make weapons that are already equipped able to be un-equipped in flight.

I have a few other questions as I test things further, I guess I should just post them here. Here goes!

More on floating hardpoints:

I wanted to know if one-poly floating hardpoints interfered with the ship's collision model (which they do, that's too bad...), so I took a model I already knew worked fine in FL and added in two hardpoints floating in space behind the ship. That worked. Then I added two more up front and things got funky. Funky like, the weapons equipped didn't fire. And then I found out why--it depended on where my ship was pointed relative to the system. If I aimed the nose of the ship at that long station orbiting Manhattan (not Newark, the one by Fort Bush's Tradelane), then the forward weapons would fire. Aim elsewhere and they wouldn't. Pressing the apostrophe key had me discovering that they were pointed to the left of my ship for some reason.

But it gets even stranger. Not only are they pointed in awkward directions, but the hardpoints themselves move about freely depending on where the cursor is aimed. I've never seen this happen--the original test didn't do anything like that. While it's a neat effect--in fact, if I could get all of them to do that behind the ship that's exactly what I want--the skewing of the firing arcs makes it useless. I've already tried making them turrets instead, and this doesn't fix the movement issue nor the firing arc problem.

This was pretty complicated... so if anyone wants me to link screenshots or have a copy of the "test model" or something, I can do that.

The problem is that most equipment is equipment, not commodities.
Don't see how you would be able to jettison an engine, shield, or any other part of the ship.

Which may be part of your other problem...
Since those hardpoints aren't on the ship, itself, they may be interfering with the ship's SUR file.
This could cause the weapons to be hitting the shields, or collision field, and that may be causing the problem.
Unless you made a custom SUR file for the ship, I doubt that the problem can be resolved.

Watch your 6!