Yeah, the .454 casull is an *extremely* high pressure round, with even more pressure than most rifle rounds in max loadings. So it has to be put in strong actions. I know that it has been strongly advised against to bore out an NEF single shot from .45 colt. Ejection is an issue too, with cases sticking in the chamber possibly. T/C Encore maybe. T/C Contender, no. I'd feel much better with a falling block or rolling block in that caliber than a break-open.
Another thing - along the same lines as above, re: the high pressures. If you do get one, I'd advise you to NOT shoot .45 colt in it, unless you clean the chamber thoroughly before switching back to .454. The fouling ring in front of the case left in the chamber by shooting .45 colt can cause the bullet in a .454 case not to release quickly enough, due to the fouling ring's "crimp" on the case mouth, which can cause the already-high pressures to skyrocket. I'd shoot .454 casull only to be safe if I had a rifle in it (and I do). I've shot .45 colts in my .454 puma, but I cleaned the chamber thoroughly since then. Not planning to shoot any more .45 colts - too risky with my bad memory as to whether I cleaned the chamber. Not to mention that the .45 colts jam a lot.