Lots of very interesting, and to my mind very thoughtful choices. And there have also been some people who are "coloring outside the lines" of the original criteria established by the thread, which specifically stated no conversions, uppers, or multiple barrels. If I am going to put in my own choices here, I feel I have to hew strictly to the guidelines, and I am also going to take on some more, self imposed. The obvious problem with my choices (and, to my mind, anyone else who didn't choose one) is the lack of a .22LR rimfire rifle, but rules are rules.
Personal criteria that fall within the overal specifications:
1) This gun's gotta hunt.
2) This gun also has to function socially.
3) This gun has to be chambered in a standard, universally available caliber.
4) This gun has to be one I've used extensively and have absolute confidence in its performance, reliability, and durability.
Ruger GP-100 6" .357/.38 (I know lots of people have used CCW as a personal stricture. This piece isn't easily carried, but it's doable in a shoulder rig. It's also quite accurate and very flexible.)
Remington 870 12. ga 3" chamber synthetic 20" deer barrel iron sights. (This gun has interchangeable choke tubes, but as this is standard with the barrel that came with the gun, technically it falls within the criteria.)
SA M1A .308. (As with many contributors to this thread, I agree the rifle was the tough one, but I'll stick with the one choice and not give alternatives.)