a shocker is an old electro gun, looks like a brick, feels like a brick etc, you will know when u see one
a cocker/autococker are exactly the same thing, just shortened, you will know a cocker if u see it because it has a back block, which when fired moves backwards and forwards on the marker, and also has 3 component under the barrel with lots of hoses attached
there is also a new shocker out which is much smaller and lighter, just do a search for them and find out yourself