I would seriously consider one of the .22 magnum pump action rifles (use to be made by Taurus in take-down version, currently sold by Henry rifle co.) Very light weight and civilian-looking (like a carnival gallery gun). Twelve shots of a very effective light-weight rounds, capable of taking small game to 100 yards, plus deer at 50 yards, plus stopping or ending the fight of bad guys out to 100 yards. Ammo is lighweight and comes in 50 round plastic boxes, just like regular .22 LR.
And if a law enforcement person checks you out, you can say, "Its just a .22 rifle" He isn't going to ask or care if its a magnum.
I am really surprised that given the parameters of the post, (i.e., slipping around for a few days to get back home in a non-instrusive manner), that the subject has drifted to multiple barrels, barrel inserts, different kinds of ammo, etc. Me, I wanna be carrying some food and water, not all of that crp.
Mannyrock