The disc is the first model of this type. It uses an orange disc. Most of them have a 24 inch barrel.
The disc extreme uses a red disc (full plastic jacket) and has a 26 inch barrel.
The disc elite is just like an extreme in the ignition but it has a countoured barrel with no open sights and it has a cantelevered lug.
The original disc is also different in that it has a monte carlo type stock.
Hope this helps.
Art