Everyone knows my preferences for heavy caliber medium vel rounds.

For backup, go for something that is either easy to reload and has a lot of rounds, or something that packs one hell of a punch. You either need the ammo to fire a lot and keep heads down, or the punch to fire once and remove a head.

Whatever you choose - practice with it. A lot.

All of the above, and more, given the appropriate target and environment.

Bring the right tool and the job will be easy, bring a wrong one and you'll have a disaster.

I like my Soviet Simonov SKS for emotional reasons. It's the only gun I've ever used, and I'd had it since I was boy. I trust it. I suppose Americans would call it a semi-automatic rifle, but to me it was always just my gun. In some countries, every boy was given a bicycle. Where I grew up, every boy had a gun.