Make your model and stuff as said in Darkstar's tutorial. Then make sure you export it with the DTS exporters that you can get in Darkstar's tutorials. Make sure you package it with everything else that is in another add-on's zip such as description.txt, server.cs, Weapon_Weaponname.cs, PNG files used on your model like said in the tutorial and whatever else you need. I would suggest making a gun edit. Don't worry, you don't need to know much on how to script to do this. Open up the gun's script and use ctrl h and replace gun with yourweaponname. Make sure you do this to YOUR weapon not the gun. When you take all the files from the gun, make sure you delete the gun's dts.