you can not make a "completely new gun" In ca due to many factors
1.) You need WEAPONS.TXT and MP_WEAPONS.txt access, which are both encrypted
2.) You need access to the CShell source code and to be able to add an ID for the game to know and to update it for everyone who plays ca to see your gun or for attributes to even know it exists
3.) Models are patched except for a select few. I don't have ca installed anymore so don't expect anything lol