Why will the Taurus Judge fire the 45Colt, but not the 454 Casull round?

I currently own "the Judge" and enjoy taking it out to the range to do some firing, but I ran across a gent who told me the Judge should be able to fire 454. I didn't believe it and have heard mixed opinions. I would just like to know EXACTLY why so that I can explain and rationalize to myself why I will go out and now try to find a 454 to have for my very own. (Always handy to have a good "excuse" for purchase with the missus!)