Periodically it’s been asserted that ’30 rounds of ammunition is more than you need in a war zone’. Not to be pedantic, but last time I was in a war zone, I had 1000+ rounds of 7.62×51 ammo linked into belts for my machine gun, 6 full magazines on my person, two more on my belt for backup, and six more in my backpack just in case. And that’s not counting a crate of spare ammo in the back of the vehicle. While a possibly irrelevant fact, I think it’s a useful comparison to the arguments about magazine capacity, and I feel like it drives home the point that no one in a gunfight ever lamented having too much ammunition.
There are four ways to neutralize an opponent; psychological shock, physical pain, exsanguination (bleed out), or incapacitation. The first two rely on the suddenly psychological deterrance of being loud and aggressive around a predator– like punching a shark in the nose, nothing surprises a potential mugger like finding out their prey is armed and ready for them. Even if a shot isn’t lethal, the pain and noise can frighten off a less determined attacker as much as 80% of the time.
But that means if you ever deploy a weapon in self-defense, there’s a 1 in 5 chance your attacker will be too mean, too high, or just too tough to be deterred by a noise and some flesh wound. That means that your only option is to stop them as a threat as quickly as possible. Every police department in America teaches this doctrine– aim high center-mass, maintain good control, and shoot until your opponent quits fighting.
Two things stop bad guys. One of them is that a bullet puts enough holes in them that they bleed out. A heart shot can cause death inside of seven seconds (sometimes). The second thing is a clean impact against the Central Nervous System (spine, brain) that can instantly incapacitate an enemy. Both of those are difficult targets to hit cleanly and consistently, particularly under the stress of firefight. It’s no wonder then that when a six-shot revolver isn’t enough to stop one determined attacker, people make the argument for larger-capacity weapons.
Despite what Hollywood tells us, gunshot wounds are very rarely lethal at the first hit. They break roughly down into ‘Instant’ (1-2 seconds), ‘Rapid’ (3-5 seconds), ‘Marginal’ (up to 300 seconds, really), and ‘Failure’. Getting shot in the pinky is painful, but rarely lethal.
There are plenty of recorded instances where a gunfight took many rounds to use. Harry Beckwith shot 105 rounds at his attackers. Sergeant Timothy Gramins fired over 100 rounds as well. The Gramins case is notable because multiple shots were considered nominally lethal at the autopsy, even though the subject continued to fight on.
Capacity laws seriously hamper law-abiding citizens and do nothing to deter premeditated murderers. While a civilian might feel embarrassed to carry a spare magazine, a killer would think nothing of a sling bag full of fully loaded spares. And when you get up in the middle of a night to check on someone bumping in the kitchen, the last thing you’ll want to do is have to fall back for more ammunition if you’re confronted by multiple home invaders (crooks do tend to work in small groups, after all). A ten round magazine might be sufficient for dealing with a single assailant, but it’s absolutely inadequate for managing multiple armed and prepared attackers.