When was the last time, if ever, that an armed civilian ever fired more than 30 rounds while engaging multiple attackers in a self defense shooting? Instead of investing in hi-cap magazines you'd be better off buying some quality body armor.
We are not talking about armed civilians in self defense shootings. We are talking about government control. I do quite well out past 1200 meters with a bolt action, but on duty in the military I always wanted belt-fed machine guns, high capacity magazines, and as many of them as I could get. As a cop, I carry high capacity magazines for my pistols and AR, an extended tube shotgun, and hope all of the officers who back me up do the same. Can we defend ourselves with a single shot shotgun, you betcha! Is it the best choice if terrorist take over the city as they did in Mumbai? Not so much. The 2nd Amendement is about protecting us from despotic governments and outside threats. Revolvers will work but you better have plenty of them loaded and ready.