You can get equal performance from other rounds that are safe so why push your luck? 
Kenny Jarret of Jarret Rifles fame gave a seminar at the recent Safari Club International convention in Reno. He made the points that the supposed benefits of the short magnums was the ability to use a shorter rifle action. When you use a short action the bullet has to be seated so far into the case that case volume is essentially decreased negating the supposed ability to equal the performance for longer conventional cartridges.
Of course in an Encore, the barrel can be chambered so that the bullets can be seated way out but the question of safety is still there. I'm also surprised that MGM is supposedly still chambering Encore barrels for these rounds. I had thought they chambered some initially and then quit doing it. Also, since J. D. Jones was heavily involved in the initial development of the Encore, if he doesn't think they're safe, I wouldn't presume to have a barrel made for one of them.
