I'm thinking about a 460S&W barrel for my encore (Katahdin barrel). I understand I could shoot 45Colt and 454 ammo through the same barrel. What level of accuracy can I hope to get with these calibers. I don't reload so I'm talking in terms of factory loads. I like the idea of being able to shoot three calibers from one barrel.Is this a waste of time or is there any value to this?

I have a 460 16" pistol barrel that the previous owner put a muzzle brake on, (now 17.5") With the brake the recoil is about the same as my 444 ported Katahdin barrel.
Accuracy with the 454 loads is close to the 460's but POI is off a little. Haven't shot many 45LC loads. Just remember to keep the chamber clean when shooting the shorter ammo.
I have several Encore and Contender barrels and frames and have been very fortunate with accuracy using non-custom barrels and factory ammo.