One caliber? Holy Christmas Trees say it'll never come to that. This is a real tough question for me since I like so many different calibers and rifles. At this point I can only say if I had to have just one, oh how I pray that'll never be, it would be either my beloved .338-378 Weatherby Magnum Accumark or a .416 Weatherby in a Mark V Deluxe. Either of them will cover anything I hunt.