Ok I've read a few things that says that a weapon mod moved over from one weapon to another, but I've also read that you can only put a mod back on the exact same weapon that it came off of. Which of these is right?

I would guess it could be tested, but currently at work!!

1. Remove mod by putting standard mod on weapon 1.
2. Check inventory to see if mod is there.
3. Check to see requirements for new mod, and write down your quantity for all the components.
4. Go to weapon 2 and add mod.
5. Check inventory to see if the mod was removed
6. Go to another weapon (#3) and see if the level of components are the same or not.

You can attach mods frome one gun to another of the same base type (pipe, bolt-action pipe and revolver pipe are different base types). If you have a fitting mod in your inventory or the workbench, this will be used, instead of creating a new one. Also the text on the bottom of the screen will read 'attach' instead of 'build'.

So, from what I've figured, you can create the most basic stuff, like "standard sights" with scrap material.

If you have a "Custom Grip" on one weapon, and you have a "Long barrel" on another, and nothing in your inventory, replacing the "custom grip" with a "standard grip" puts the custom grip in your inventory to use on the "long barrel" weapon so now you have both on that weapon.

I am NOT sure if simply scrapping the gun puts mods into your inventory or simply destroyes them.

Thanks will have to test that out tonight!

So you can drop mods on the workbench?

I would hope that they make it when you scrap a gun or weapon you would get all the non standard mods from it, but I currently think it just gives you the basic stuff.

It has to be the exact same weapon base type. This can be confusing because sometimes the name of the weapon can obscure crucial facts about the weapon. On top of that, some weapons that seem really different are actually the same weapon. You also can't strip a weapon for parts, you are forced to spend resources to build another part to replace it with, and these parts are heavy.