Rossi makes a variety of 5lb lever guns in 44Mag and 454 Casull. I don't see how the Ranch Hand stock would work for bear defense, I assume you change out the stock. Pity about the restricted Judges, they are super light.
So
4lb Rossi Ranch hand 44 Mag +new stock, maybe an extra half pound
5lb Rossi M92 Carbine .44 Mag/.454 Casull.
I know firing the hypothetical pump 5lb 12 ga would be worse than the bear, but 2lb of supplies might be more likely to save my neck than a gun. A 5lb .454 Casull would rattle my fillings enough, I suppose.
You could carry 44 special/45 Colt for small game I expect.
Edit:
My brother organised a lot of adventure Racing in the UK, is now a landed immigrant, and is horrified by the weight of my 7lb Grizzly (Even though he was used to the SA80). He budgets every pound, and bear defense is a low priority. Although, he was sleeping beside a stream in BC when he heard a splash. He thought "Bear!" and (as a good UK citizen does) reached for his iPhone. He show me a couple of black photos. It was just a fish jumping.
He needs a bit more firepower than the iPhone, maybe I can sell him on the 4lb Ranch hand

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