You can't do that. In order to rechamber a barrel to the same AI caliber the barrel needs to be set back. Obviously that's not possible with an Encore. What you can do, though, is make it a 222 Rem magnum (regular or AI) or a 22-250 or my choice, a .225 Winchester. You just have to pick something longer than the existing chamber so it'll clean up what is there. If you go running a 223 AI reamer in that barrel you'll end up with a chamber that's neither here nor there and is not safe to fire factory 223 in, the whole point to the AI rounds to start with.