I know this thread is old, but I enjoy these kinda threads so I'm going to add my two cents.
FN FAL - .308 Winchester
Sig Sauer P226 - .40 Smith & Wesson
Mossberg 500 - 12 Gauge
As far as ammo any think any big name calibers will be relatively plentiful, .308, .223, 7.62x39, 9mm, .40, .45, etc oh and of course 12 gauge and .22. So I don't think that anything major will be a real issue, relatively speaking. I'd want a semi-auto type .308 because of the versatile range and effectiveness of the round on anything from humans to elk. The .40 well just because really, I wouldn't really sweat 9mm, .40 S&W, or .45 ACP they'll all smoke check someone effectively. Can't think of any logical reason to pick anything other than a 12 gauge, but I do think the pump action shotguns out there are more versatile than semi's. You can get barrels and accessories to convert a Mossberg 500 or Remington 870 to shoot everything from ducks flying so high they need oxygen masks to people, hell some companies even proclaim to produce dangerous game loads. Remington 11-87's, Benelli M2's and the like while sure you can probably switch a barrel on them as easily as a pump the options simply aren't as readily available as the pumps, plus they don't offer you the ability to run low powered rounds effectively.
Here endith the lesson. I love that movie
