I will note that the original poster was asking about a .22 carbine for HD.
I invite anyone who thinks 6 shot from a 20 gauge at 10 feet is not a viable defense round to stand in front of one. My anecdotal experience is that being shot with a small caliber bullet really didn't hurt too much at the time, and didn't really stop me from functioning.
If you don't like it, if you aren't comfortable with it, by all means, use buck shot. The point is this: I'd take a small, light, reliable shotgun over a .22, for the OP.