Put this in the description.ext file, note that you will only be able to select the weapon once you have PBOed it and put it in the missions Folder
class Weapons
{
class Gunname { count = 1; };
class Othergunname { count = 1000; };
};
class Magazines
{
class magazinename { count = 6; };
class othermagazinename { count = anynumber you want; };
};