56Subject: 9mm bullets are dangerous.
However they are a handgun round. They’re less aerodynamic and have less power coming out of the barrel. They’re not designed for long-distance flight.
7.62/.308 and 5.56/.223 are rifle rounds. They have more power out the barrel and are designed for long- distance, accurate engagement.
buckydean: I think the ELI5 would be that the size of the gunpowder charge behind the bullet is what makes the difference. I could take any of those bullets you listed and throw it at you, and it’s not gonna do much damage. Rifle rounds have a much bigger gunpowder charge behind them, which makes a bigger boom, which moves the bullet faster, and a faster bullet has more energy to transfer to soft bodily tissues. A lot more still comes into play though, like what material the bullet is made from, how far the bullet travels, and where you are hit.
mmmmmmBacon12345: Diameter of the bullet isn’t the only dimension that matters.
The 9mm bullet is larger in diameter than the two rifle rounds, but has significantly less energy behind it and is lighter than the 7.62 bullet. The rifle rounds have a lot more gun powder packed behind them so they leave at much greater speed and can deliver a lot more energy to the target.
[Look at an image of the various rounds](http://www.prep-blog.com/wp-content/uploads/2013/01/22lr-9mm-556.jpg), the two on the left have the largest diameter, but the two on the right have a lot more *Boom* behind them to get them to the target. The far right round is the 7.62 that AKs use, the NATO 7.62 is significantly longer
StupidLemonEater: Strictly speaking, a 9mm bullet (~8 grams) has more energy than a 5.56mm bullet (~4 grams) and will therefore do more damage *if they are moving at the same velocity.*
That last part is a big caveat. If you just look at the two cartridges, you’ll see that a 5.56 rifle round has much more propellant than a 9mm pistol cartridge. Also, a rifle’s barrel is longer which means the bullet has a longer distance over which to accelerate.
What matters is the mass of the bullet *and* the velocity at which it flies. Gun types express this as “muzzle energy” which is 1/2mv^(2) (m being the bullet mass and v being the velocity as it leaves the barrel.)
Depending on the gun, a 9mm bullet has around 600 joules of muzzle energy, where a 5.56mm has around 1800 joules. This is a closer analogue of what kind of “damage” the round does but that also depends a lot on the target.
ChopperHunter: OF the three 5.56 is actually the least dangerous. It was designed by NATO to increase the chances of wounding rather than killing. Therefore 5.56 are likely to produce through and through wounds and they rarely fragment or tumble. They were designed this way because NATO did the math a figured out that a wounded enemy soldier who has to be evacuated, given medical care, fed and sheltered costs the enemy many times more resources than a soldier who dies on the battlefield.
On the other hand 9mm and 7.62 were both designed to kill. Therefore there are prone to fragment, tumble, and become lodged inside the victim.
D0ngl3: Additionally, .223 has a greater powder-to-weight ratio so it’s a more energetic round. 9mm became popular because the round’s shape allowed for compact magazines though the FBI thinks .40 S&W is a superior field ammunition.
The 7.62 NATO and .223 are considered more “humane” rounds because it takes an an average of 4 shots which punch straight through to down a solider. If you get hit with a single .45 round there’s less kinetic energy behind it but each hit will arguably do more damage because of the bullet design and ballistics upon impact.
AMooMooCow: Everyone’s talking about kinetic energy, but no one mentioned the initial contact area of the tip of these bullets on impact. A rifle round has a sharp tip and a 9mm is way fatter. The reason materials fail is due to pressure, or force over area. Force can be defined as the change in velocity over time. So the more kinetic energy that is released from the bullet to break flesh or armor, and the smaller the area is before deformation, the more damage will be done.
Because F/1 = Pressure, but F/0 = infinite Pressure, so imagine the damage of a 9mm bullet with the same energy of a rifle round and a fat head doing the base damage, but the rifle round point would be on the order of 1/100 or whatever as much contact area, so F/(1/100) = 100x the initial stress on the contact area