where do you save new guns to?

[V-Man]

Long story short:
It needs to be unpackaged in your \mods\ folder, in a file structure otherwise identical to the weapon you are modding.
Example:
To mod the assault rifle, you look at its directory structure:
[AssaultCube home folder]\packages\models\weapons\assault

So the assault rifle mod should be unpackaged under
[AssaultCube home folder]\mods\packages\models\weapons\assault