Shot skeet for many years in the Military with a Mossy 500 pump. 26" is the prefered lenght. A pump is not the best for skeet almost all the really good shooters used O/U or semi-auto's . An 18" barrel is just another disadvantage- shorter site radius. You could do it maybe even become good at it, it will be just more of a challenge. If your thinking a fixed cylinder bore forget it! You must have atleast a mod choke- skeet choke preferable!
Now all I have are semi-auto's an O/U's for shotguns -wish I would have had them back then for skeet!