What does caliber have to do with stopping power of bullets

All this talk about how bullets kill “us”, and about force vs. kinetic energy, remind of something I’ve always been unclear about. What does the caliber of a bullet have to do with its ability to kill/maim/stop?

It seems to me that a bullet’s stopping power is determined by its energy. And that, the energy, is a function of the amount of powder or whatever in the cartridge. So I will ask: For identical degrees of powder (or whatever) in the cartridge, would not a 22 caliber and 45 caliber bullet have identical stopping/killing power?

I’m almost positive that caliber refers to the bullet’s size. As inertia=mass * velocity, a heavier bullet would hit with more force.

The amount of powder in the cartridge isn’t equal. A .22 cartridge is smaller than a .45 cartridge.

Slight correction: I think that caliber actually refers to the muzzle size. So if a .45 has a bit more than twice the diameter of a .22, its mass is at least a few times greater.

Stopping power of any given round is a function of its speed, rifling, weight, caliber, deforming characteristics, and to lesser extents its shape and composition.

A bullet’s stopping power is basically its ability to effectively transfer its energy to the target causing damage. Let’s take each of the characteristics in turn:

Speed – The faster the bullet the more energy it has. Therefore the more energy it can transfer. The downside is that the quicker the bulet, the less time it can spend “in” the target. The target may not be able to contain the bullet, in effect allowing the bullet to pass through the target without transferring much of its energy. .22s move quicker, generally that .45s.

Rifling – the amount of rotation a round has when it leaves the barrel of the gun. The quicker the rifling, the more the round “drills” into the target. The drilling action allows the bullet again to pass through the target without transferring much energy.

Weight – The heavier the bullet, the more energy it carries (gives the bullets being compared are moving at the same speed). This is easy to prove: a heavier round needs more powder to propel it as swiftly as a lighter round. Hence, a heavier round has intrinsically more energy to transfer to the target.

Caliber – The size (diameter) of the round. The more surface area of the bullet, the better able it is to transfer its energy to the target.

Deforming characteristics – The most important factor in transferring energy. Bullets are designed to deform after hitting a target. In effect going “splat”. Hollow-point bulets are perfect examples. They are designed to pancake out after penetrating the target, braking the bullet within the target and transferring just about all its energy to the target (some heat energy would be lost though).

Shape – If the round doesn’t deform, its shape would determine how much energy a bullet would transfer. A needle-nosed round would transfer less energy than a flat-nosed round.

Composition – Lead goes “splat” easier than copper or bronze. Copper jacketed rounds “spit out” their lead innards. Telfon-coated rounds (designed to penetrate body armor) will just drill a nice, neat hole through its target if it is unarmored.

So you see Karl, the ammunition manufacturer has a lot of variable to deal with when developing bullets.

In general, a .45 round has better stopping power than a .22 “if they are both moving at the same speed” because it’s heavier, has more surface area and a larger round will deform easier. In order to answer your question we are not bringing into play composition, rifling, deforming characteristics or shape, or assuming they are the same for both the .22 and .45 rounds.

IRL, of course, this would not be true. The .22 would be moving a lot faster, wouldn’t be jacketed, wouldn’t mushroom or pancake and would have a tighter rifling each of which would significantly affect it’s stopping power.

Here’s a quick rule of thumb: with a .22 you need a head or heart shot to stop someone from charging at you. You hit 'em in the stomach with a .22, they’ll keep coming.

If you get winged in the shoulder by a .45, you probably be spun around and knocked down.

To pick nits, mass times velocity is linear momentum, not inertia.

Calibe has everything to do with size, if you want stopping power get a more powerful load like say a magnum load. Of course the larger the shell the more momentum it carries.

Yeah. What I fuckin’ said, horsefat.

Muzzle energy says how powerful a bullet is. mv2. So velocity is far more important than mass. BUT, if the bullet goes right thru you, it has not imparted much of it’s energy to you. this is why bullets with large calibers/diameters have higher “stopping power”, irregardless of mass/weight. Bullet type, as Scotty says, is also important in haveing the bullet impart its energy to its target. Bullets do not impart enuf energy to a human to “knock you down” this had been tested with freehanging sides of meat, a .45 barely makes them move. What does the “knock down” is the pain & shock.

the big arguement is between .45 & 9mm. I’m a .45 man myself. (9mm are faster, thus more energy, .45s are bigger, thus more stopping power. I don’t want to get hit with either :smiley: )

A cop buddy of mine was hit with a 9mm in his vest. Cracked a rib, drove the wind out. He said it felt just like being hit with a (hardball) fast ball.

From what I gathered during some training sessions with the police, “stopping power” is more a question of the trauma inflicted on the body than on the energy transferred.

I expressed my doubt, and they gleefully showed me a disgusting video of (part of) the autopsy of a gun shot victim, who had “stopped” two bullets (i.e., they were still in his body) and kept charging. The bullet that actually stopped this fellow went straight through him, perforating his aorta (I think it was) on the way. Arguably, the killing bullet left less energy in the victims body - but it was the one that stopped him.

But I have a feeling that this a very old debate…

This is a very old debate, and also something of a can of worms. An interesting and informative site is


which argues fairly convincingly that handguns don’t do much more than punch holes through people. Larger calibres have greater penetration (bullet mass increases with the cube of calibre, whereas cross sectional area increases with the square) and so are more likely to penetrate through to something important. Larger calibres also make a bigger hole and so will cause more rapid blood loss.

The site is very down on the idea of energy transfer as a stopping mechanism, pointing out that collisions in many contact sports actually transfer more energy than a typical bullet impact! It recommends large calibre bullets of moderate expansion, since these make a big, deep hole.

There are other sites which strongly promote the idea of energy transfer. An example is


This site recommends high velocity, medium calibre rounds with large expansion since these dump K.E into the target the fastest.

Which is right? The real problem is getting good data - a centre-of-mass hit with a .45 may be less effective than one with a .22 if the .22 clips the aorta and the .45 doesn’t. I tend to favour the “punching holes” side of the debate, but really the jury is still out on this one.