Are rifle-caliber pistols the ultimate backup guns?

A pair of aces. These two weapons share magazines and ammunition, greatly simplifying the logistics involved in keeping them fed. (Photo: Jim Grant)

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Since the Bureau of Alcohol, Tobacco, Firearms and Explosives gave the okay for shouldering a pistol brace, shooters have been buying AR and AK pistols in droves. Which is strange because rifle-caliber handguns are substantially less accurate, more difficult to aim and have egregious muzzle blasts compared to their full-sized counterparts. But, if these weapons are truly inferior in every way except size, why are people buying them?