In my view, setting aside the fact that a shotgun or handgun *may be* a better option, if one does set up a rimfire rifle for self-defense, it ought to be a pump or lever-gun, not a semi-auto, since *the* primary failing of a rimfire for this purpose is not lack of power (though there's that too), but rather the unreliable ignition of rimfire priming compound, since it doesn't always get spun out into all parts of the rim.
This is my concern also.