This has been discussed many times before and it makes the most sense to have a 20g single shot with 22lr adapters. 20guage, for some odd reason, seems to play nicer with adapters than 12g. Some speculate it has to do with the thinness but who knows for sure. I find it's hard to get POI with 12g / 22lr adapters but with 20g it just works. The H&R Tamer will break down into a backpack easily, and it's $159.00 at WSS with a nickel finish. That's the backpacking / survivalist / do everything gun. I was using a Savage 24 combo gun but I'm selling mine in 357/20 and getting a Tamer
Some people may recommend going with the 410, or even 22lr / 410 combo. The second you see that, ignore everything they say, do the same if they mention 357magnum or other pistol cartridges. What you want is one large, hard hitting round, that's commonly available wherever and a whackload of smaller ammo. You can pack along your pistol cartridges with adapters, it doesn't really make any sense when you have a 20g, but if it makes you feel better. What you really don't want is a whack of heavy 150-230g pistol cartridges that add a bunch of weight, and can only be used on medium sized game or larger, but don't have the sheer stopping power of a 20g slug. 44magnum isn't bad, but once again, it's not super common and it's heavy. You could use it as a substitute for 20g slugs but how will you shoot 22lr.
The other thing to consider is the durability of the gun. A single shot 20g is as reliable as it gets, and the fact that it takes down into a 19 inch long package gives it the edge over bolt guns. Keep in mind that a 7/8th OZ slug out of a 20g is a 382g projectile going pretty fast, which is great stopping power.
If you want heavier ammo, you can go with 12g, but make sure you do the tests with the adapters because I have found the accuracy to be terrible. It's not just myself, articles that I have read show that I'm not alone and that the 20g just seems more accurate. If someone knows why this is, it would be nice to know lol
EDIT: One thing I forgot to add, there's also a few people who favour taking only a 22lr rifle. I've done this before with an AR7 and bearspray, works well. You basically leave it taken down until you come across a grouse or squirrel. Usually those animals are so stupid they will stay put until you've quietly assembled the gun and killed them. I got 4 grouse last year this way in one day while walking around some backtrails I found in the middle of nowhere. There are a lot of AR7 haters that exist, and I understand why, but it fits the niche that Henry markets the gun for and it has never let me down. I've only owned it for 2 years though, we'll see what happens 10 years from now, my guess is that it'll still be fine.
