Update
I had to revive this thread after an expansion of my mini-epiphany on the best "wilderness survival gun", for sheer/strict food acquisition.
Earlier in this thread, I expounded at length at why a rimfire with shotshell would be the best idea since literally the most plentiful food source by far, in terms of ease to obtain with gun, is (what I'm calling) "tweety birds". You can sit still for 5-15 minutes and get a shot or two at some little bush songbird. Not much meat, but it's some protein, and you could collect 5 or 10 songbirds for every squirrel or other small rodent you kill. So the idea of a rimfire barrel or rimfire chamber adapter in a .223 is good to an extent, but ultimately not satisfactory because it will spin the shot and give you a poor donut pattern, and cause you to miss. Also, anything larger than a .22 long rifle with shot will destroy too much meat on these already thin-on-meat critters, so even a .38/.357 shotshell would destroy too much, for example, not to mention also have the rifling problem if fired from a pistol.
So the more I think about it, the more I think that the answer must be a 3-barrel custom drilling - it just has to be a drilling for the ultimate efficient food-gatherer, and one of the barrels must be a smoothbore .22lr "garden gun" barrel.
So, here's what I'm thinking: Two rifle barrels side by side, on top of one centered 12 gauge shotgun barrel below.
The 12 gauge shotgun barrel will kill anything from deer to ducks with various ammo:
-Birdshot for birds large and small on the wing, or pot-shot, or for turkeys
-Buckshot for deer or whatever
-Foster Slugs for deer, elk, bear, hogs, and other various/sundry tasty ungulates.
The 12 gauge may very well cover all your needs, and really does cover all your needs except: small critters such as tweety birds, squirrels, etc. (due to excessive meat damage), and long-range needs. This would come with of course multiple choke tubes. 3" or 3.5" magnum chamber.
So, the Upper Left barrel I think must be a smoothbore .22 lr, as I mentioned above, for tweety birds and even pot-shooting doves, quail, and the like. I think up to 75% of your non-fished meat can be such small to medium sized birds, all "pot-shot".
The Upper Right barrel needs to be a centerfire with one or more sub-cartridge chamber inserts, and I've really got two options for this barrel: Either a .223 Remington, 1 in 9" twist, with chamber inserts for .22 magnum and .22 long rifles. So this barrel could handle .223 Rem with all its many variations of ammo, plus .22 shorts, longs, long rifles, Aguila SSS 60 grain penetrators, and even Super Colibri ammo, and also all .22 magnum ammo with the other insert. And with a headshot, a heavy .223 Rem bullet could bring down an ungulate with ease, though it's a bit marginal for vitals shots on large ungulates. The other option is a .308 win or .30-06 barrel, with chamber inserts for .32 acp, .30 carbine, 7.62x39 or .30-30, or even .32 H&R mag and other calibers. This would be really versatile, but not handle the cheap and plentiful (and light to carry) rimfire ammo (.22 lr and .22 mag). It would also handle long-range duties better than .223 rem, esp. for vitals shots on large ungulates and bear, etc.
So our choices are:
1. Smoothbore .22lr / .223 Rem / 12 ga 3.5"
or
2. Smoothbore .22lr / .308 win or .30-06 / 12 ga 3.5"
Which one? Or, OR, the ultimate may be a rifled .22 barrel instead of a smoothbore, BUT with one of those "choke tubes" such as are found on the H&R Survivor and T/C encore bbls in .45 colt / .410 shot, which are really not choke tubes, but tubes with "straight rifling" which "un-spin" the shot, giving it a good pattern. So that would bring up choice #3:
3. Rifled .22 magnum with an "un-spin tube insert" for the muzzle and a .22lr chamber insert / .308 win or .30-06 / 12 ga 3.5"
Which of these 3 drillings, and which .30 cal centerfire (.308 or .30-06)??
I really suppose the ultimate is #3 in with .30-06, *if* the unspin insert thing really works to throw a good pattern. If so, with chamber inserts, you'd be able to shoot in this 3-bbl gun, all effectively:
1. .22 s, l, lr including SSS (chamber insert in .22 mag)
2. .22 lr shot (chamber insert in .22 mag)
3. .22 magnum
4. .22 magnum shot
5. .30-06
6. .308 Win (chamber insert in .30-06)
7. .30-30 Win (chamber insert in .30-06)
8. 7.62x39mm (C. I. in .30-06)
9. .30 carbine (C. I. in .30-06)
10. .32 H&R Mag (C.I. in .30-06)
11. .32 acp (C.I. in .30-06)
12. 12 ga 2.75" (bird, buck, or slug)
13. 12 ga 3.0" (bird, buck, or slug)
14. 12 ga 3.5" (bird, buck, or slug)
15. For that matter, with chamber inserts, also shoot .300 whisper, .300 savage, etc., but I think the .32 acp / .30 carbine / 7.62x39mm / .30-06 foursome would make sense to cover all the bases. I'm guessing a 1 in 10" or 1 in 11" twist would work for the .30 cal bbl.
What say you? Who do you think I could commission to make me this drilling? Is it possible to do under $7,500, do you think? I'd want the 12 ga regulated to the point of aim at 30-35 yards, the smoothbore rimfire regulated to 10 yards, and the the centerfire regulated to around 150 yards.
It kind of ends up being a "Mr. Potato Head" gun, doesn't it?