Eley VIP are a cheddite hull, most manufacturer use cheddite hulls! if you want a tight fit, get an unfired shell as the brass (which is actually steel) expands to the inside of the shot gun chamber once its been through the gun! any heavier shell such as game shells or magnum shells will have longer brass on them as they are more expensive, clay shells tend to be made on a budget so the brass is very short!
Shot gun sheels run up to 3.5" for waterfowl shooting, some of the longer ones would be interesting for projects. Waterfowl shooter might be able to give you bigger 10g or 8g shells as well!
The brass (steel) rusts like a 1982 nissan micra so a good idea is to treat them with oil or car polish to stop the water sitting on them, they will last a little longer!