Dude, it sounds like you may not know exactly what a weight gainer shake is. It is usually a whey protein, high carbohydrate (malto or dextrose). The carbohydrate content is so high so that it will contain an abundance of calories. When it says that there are 480g or carbs in 3 scoops, that is entirely possible.
If you want my honest opinion, stay away from weight gainers. Stick with a basic whey protein shake if that is what you are looking for, especially pre-WO.