Yep, talk to the guy who would do the reboring. He'll tell you what's what. Assuming this is a 219 barrel being discussed, my gut says that .45 Colt is probably too big. As far as will a 219 hold the .357 Maxi, I should think it would since those things can be found in .30-30, and I've heard tell of .30-30's being re-chambered to .30-40 Krag. But it's not about "strength", it's about practicality and utility.
Naturally the first question to resolve is if the gun is in sound condition to accept a conversion to a hotter/fatter cartridge. Is the barrel "on face" to the standing breech (headspace in other words)? Locking mechanism not worn to crap? Firing pin hole and breech face not eroded? Can you alter/install a new extractor?
Of course, if it's the same barrel you started this thread with, again it could easily all be a moot point if your threaded holes are too deep. What may be "sorta/kinda ok" now with a .22 bore and Hornet chamber may get dicey if opened up to .35-.45 caliber. Even then if it holds ok you're then still left with a miserably thin safety margin. Think! Think! (And please don't make your next question be "Can I fill the holes to avert that?")
