If you are wondering why you cannot see new attachments appearing in your for example regular cw2.0 ar15's customization menu, read this.
CW2.0's parameters of how attachments will occur and work on a weapon are defined in the WEAPON'S LUA file. This means you must decompress the gma file, find the lua, and write something to it. So:
1. If you have no idea of how to make a cw2.0 swep, either learn it or unsubscribe to my addon until someone on gmod create a weapon which uses attachments in this pack;
2. If you are a developer, I'm sure you know what to do. So just enjoy it and make critiques.