In my last article, I pointed out that successful bystander intervention against a spree shooter reduces the average number of fatalities from about 14 to about 2. Here is a first hand account by a survivor of a spree shooting that killed 23, including both her parents, describing how gun control laws prevented her from intervening:
Now, spree killings are responsible for such a small percentage of all murders that this is a weak argument against gun control, though it certainly isn't an argument in favor of gun control. More important, perhaps, are Ms. Hupp's argument against limiting magazine size - magazines can be changed out in less time than it takes to aim one shot, and murderers are more likely to carry spare magazines than are law abiding concealed carriers - and her argument that ultimately, the purpose of the second amendment is to ensure the population has appropriate weapons available to resist the government should it become necessary.
2012 post on fatalities in spree shootings when ended by police versus when ended by bystanders:
2008 post from before the Supreme Court second amendment ruling in Miller pointing out the amendment's purpose of allowing the citizenry to resist government: