I think that a survival gun should be chambered for common ammo, ergo my 12 gauge and 30-06 preference in North America. I'd prefer 16 gauge as it would contribute to a smaller/lighter package, but 16 gauge ammo is much harder to find anywhere in the U.S. that I've traveled to than 12, 20, or even .410. Every drilling that I've handled has been less handy than a comparable O/U combination gun. A single firearm with 3 or 4 barrels strikes me as a compromise that, like a SAK, is a nice concept but not very practical even when the design is well executed. If you think that you need to shoot .22 MAG snake shot, a chamber insert for the rifle barrel would probably work.
IIRC, a lot of survivalist recommend using mouse/rat traps like the Victor Metal-Pedal style to collect small rodents for meat.
IIRC, Dick Proenneke's primary firearms were a 357 MAG handgun, a 30-06 rifle, and a 12 gauge shotgun.
Since everybody has had different experiences, you're going to get a lot of different opinions/perspectives, few of which are likely to be in complete harmony with your's.
BTW,
www.mcace.com appears to be gone, so MCA chamber adapters and inserts are no longer available unless somebody else has taken over that market niche from Ace Dube in Anchorage..
