.44 mag with 300 grain hornaday xtp, is an excellent start, my bias is toward a S&W model 29 or 629, but the Ruger Blackhawk and Super Blackhawk are very accurate single action firearms with that bullet weight and less expensive, the Ruger redhawk is a very fine pistol, but not to my taste in grip and sighting system, although if you get one with the built in integral ring system can be be a very accurate and reliable pistol as well. The .45 long colt, with 300 grain bullets will do a great job as well, you just can't buy the ammo you want as easy.
.454 Casull, will definitely do the job, if you can afford the revolver, and you will not be disappointed, if you buy the Freedom arms model.