Geez, guys, I'm sorry that I just cannot agree with any of this. I have been hunting and shooting, with shotguns and rifles, for 42 years.
Buckshot is devastating or effective out to 60 yards?? Sorry, but it isn't. It wouldn't come close to the effectiveness of 3 shots of solid point .22LR fired from a semi-auto rifle. Numerous tests of buckshot have been published in articles in G&A, American Rifleman, etc. over the past 20 years, and they have universally found buckshot to be a loser past 35 yards, no matter whether you are shooting 00 Buck or #4 Buck. It is such a loser, that it has been outlawed in many states, including southern states such as Tennessee, as being inhumane on deer.
The problem with a shotgun is the extreme weight of the ammunition, compared to its effective range. I have not done any actual weight comparisons, but for the weight of one high base 12 gauge shell, you could probably carry 20 rounds of .22 LR, or 10 rounds of .22 Magnum, or 3 rounds of .223. And, your range with these is not limited to 40 yards. (I was accidentally hit with a blast of #5 bird shot from a 12 gauge at about 60 yards one time, full front on, while rabbit hunting. It just bounced off my wool hunting coat. Didn't even scratch my glasses! A .22 LR solid from that distance may well have killed me.) Yes, a 20 gauge shell weighs somewhat less than a 12, but probably only 25% less.
Yes, I know that slugs are effective on deer out to 100 yards. I have killed a deer at that range with a 20 gauge slug. But, the weight of slug shells is very considerable. (How many boxes of those are you gonna carry?) Instead of a slug shell, give me two or three cartridges of .223 soft point or 10 rounds of .22 magnum any day, and I'll just limit my shots on deer to 50 yards.
Yes, a shotshell is more effective if you are going to shoot at moving game. But, honestly, in a shtf situation, are you really really going to waste a shotgun shell by shooting at a flying quail or a running rabbit? Better not shoot at many of those, as you will only be able to carry 2 or 3 boxes of shotgun shells. For that weight, you could carry an entire brick (500 rounds) of .22LR, and limit yourself to sitting game.
I just can't imagine a shotgun of any gauge being a good shtf weapon if you are going to hold up somewhere. A child with a .22LR repeater would able to pin you down and put you out of commission from 100 yards away. He could literally rain Heck down on you, and you would do what? Fire a slug at him?
Now, I can agree on the shotgun in one scenario: I would agree that in a deep urban environment, where you had to move from room to room, or building to building, a good 12 gauge repeater, with 3 inch shells in #4 buck would be a good bet. But, don't let yourself get caught out in the town square or any other open area in town. Anyone on a roof with any type of rifle would be able to nail you.
Give me a .22LR semi-auto, or a .22 magnum repeater, or even a single shot .223 rifle any day, as either a hunker down gun or a foraging gun in a shtf situation, over any shotgun.
Of course, these are just my silly opinions. No offense intended to anyone.
Mannyrock