Statistically, 90 percent of shootings take place within 7 meters. In modern war, this statistic is inverted: 90 percent of shootings take place outside of 7 meters. Also, a melee weapon, or no weapon, is more effective than any gun within that range of 7 meters (unless a derringer comes into your hand from a rig on your wrist, or you are ready with a cowboy quick draw holster), assuming weapons are not drawn at the start of the encounter.
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most handgun calibers are too small to kill a human reliably. With an equipped medic nearby, only one in ten hits are fatal (this does not include .357 magnum which is actually perfect for killing humans). This includes large pistol calibers like the .50 and the .44 which "over-penetrate" making them far less effective than a 9mm or something similar.