What Determines Bullet Lethality?

[Nick R]

Perhaps this question involves too many factors to consider and lends itself to being overly speculative but...

What would seem to be the most important ballistic property of a bullet in determining lethality? (coming from another forum trying to get an answer from a more qualified group - question has come up in the past a few times with no one giving a very good answer)

Muzzle velocity, energy and bullet weight are typically published figures. Many people seem to say bullet weight is most important (maybe suggesting that bullet momentum is the key factor?), others say a high caliber is most important, etc.

After thinking about it for a while I've come up with 2 factors I would think would be most important for immediately destroying a target.

1) Projectile energy
2) Projectile expansion upon hitting target/projectile size

My thinking on these 2 is the projectile will develop high power since

power = (force * distance) / time
where force is force exerted on target by projectile

The projectile expanding on contact with the target would cause in increase in df/dt, resulting in higher peak power (but trailing off more rapidly as due to more rapid loss of velocity).

So since there would be higher peak power, or higher rate of energy transfer, I would think this would be analogous to torching a piece of meat to crisps in a few seconds Vs. heating it in a crock pot for a longer time. Of course that brings the question exactly what sort of damage will that energy cause, if any...

This would lead me to believe that large, light, extremely fast bullets that expand to large sizes rapidly should do the most (immediate) damage...

Can anyone provide insight?

Again, sorry if this is too speculative but there are many myths in this area. It would be nice to know the truth.

 

[mgb_phys]

I suspect that the maximum muzzle velocity of a bullet is fixed by the chemistry of the charge as well as practical factors like barrel wear.
In this case the way to increase the energy of the bullet is to make it larger.
The lethality of the bullet probably depends on the amount of energy available and how much/how quickly the energy can be transferred intot he target/victim.
There are probably also anatomical factors about the depth the damage is spread into the victim.

 

[DaveC426913]

"...the most important ballistic property of a bullet in determining lethality?..."

Accuracy. :-)

Without it, your lethality is zee-row.

 

[Nick R]

Well yeah... accuracy is important.

Being one who makes my own ammunition I can say that, maximum velocity is largely dependent on what weight bullet you use (there are many weights available for the same caliber .45 auto for instance varies from 185 gr. to 230 gr.) and how long your barrel is. Casings are generally not filled all the way up with powder so that isn't a limiting factor (.45 auto for instance are only filled halfway for a max charge with the type of powder I use).

Stats from my manual with the maximum powder ->

185 gr bullet (0.012 kg) -> 1050 fps (320 m/s) -> 610 J
230 gr bullet (0.015 kg) -> 880 fps (270 m/s) -> 550 J
*Pressure for both is just under 18000 CUP

Common thought says the heavier bullet is more effective, though it carries less energy.

 

[olgranpappy]

This would lead me to believe that large, light, extremely fast bullets that expand to large sizes rapidly should do the most (immediate) damage...

Maybe so, but you might not be able to find a material that is both as light as you would like and still strong enough to be fired without deforming. For example, a marshmallow is both large and light, yet you would not be able to make a bullet out of it.

 

[berkeman]

Stats from my manual with the maximum powder ->

185 gr bullet (0.012 kg) -> 1050 fps (320 m/s) -> 610 J
230 gr bullet (0.015 kg) -> 880 fps (270 m/s) -> 550 J
*Pressure for both is just under 18000 CUP

Common thought says the heavier bullet is more effective, though it carries less energy.

Interesting numbers. Is there an optimum bullet weight for each barrel length (given a fixed max chamber pressure) that gives max muzzle energy? Like, what does a 150 gr bullet do under the same conditions?

Also, are you asking about "lethality" in terms of an animal-type target (human, deer, etc.), or are you speaking more generally like against vehicles and other mechanized things? For animal-type targets, you already mentioned expansion characteristics, which I think are documented fairly well for different types of bullets. Comparing Glazers, hollow-points, and standard jacketed rounds, you get way different wound cavities.

So if you mean against animal/human targets, then it will come down to energy transferred during the impact and expansion quality. The energy at impact depends on the muzzle energy, and how much of that energy is lost due to wind resistance. The heavier the bullet (given the same shape), the less energy it will lose in flight. If you could find a good equation for the force of wind resistance on different types and weights of bullets, you should have enough info to maximize the "lethality" at impact.

Kind of a grizzly subject, actually. BTW, Quiz Question -- how come both military and police rounds are not chosen for maximum lethality? Slightly different reasons, actually.

 

[rcgldr]

You'd get better answers from a weapons oriented site. A co-worker of mine was into this stuff.

Damage is related to how much energy is released by the bullet. The fluidic shock wave is where most of this energy goes. So the most efficient bullet is one that effectively explodes (or tumbles) inside the target without exiting.

There are video examples of water melons being blown up by medium velocity bullets, while hardly being affected by high speed, hard nose bullets that just pass through leaving a small hole.

This is different than lethality of a projectile. This ranges from slow bleed-out to exploding internal organs from the shock wave to dismemberment. Getting hit by a 1ton+, supersonic, 18 inch shell, from a battleship cannon would certainly be lethal, but not the most efficient. The Apache's M230 chain gun will also get the job done (although mostly used against vehicles, they've been used against personell as well since it's the only gun on the Apache). If you're into gore, there's are night vision videos (black and white) of them in use during Desert Storm, but I'll leave it to those interested to do a web search for this stuff.

Link to Apache's gun.
http://en.wikipedia.org/wiki/M230_Chain_Gun

How come both military and police rounds are not chosen for maximum lethality?

Military - weight (soldiers have to carry these), plus sometimes it stated that wounding a combantant is better than killing one, plus Geneva Convention has rules about the bullets allowed for combat. Snipers do use close to maximum lethal weapons. Police - they don't wan't bullets going through their targets or walls. However, the FBI was using 10 mm auto pistols, before downgrading them a bit since the weight and kickback were difficult for a smaller person to handle.

 

[olgranpappy]

BTW, Quiz Question -- how come both military and police rounds are not chosen for maximum lethality?

perhaps another reason is cost? and perhaps yet another reason is irony?

 

[berkeman]

perhaps another reason is cost? and perhaps yet another reason is irony?

No, Jeff nailed the quiz question. He even gets extra credit for the sniper thing -- I hadn't thought of that angle.

 

[Nick R]

Thanks for the input.

As for more quiz question answers, FMJ rounds feed more reliably in a lot of weapons. They also penetrate soft body armor/flak jackets more efficiently assuming they don't have plates.

 

[Dr. Courtney]

Perhaps this question involves too many factors to consider and lends itself to being overly speculative but...

What would seem to be the most important ballistic property of a bullet in determining lethality? (coming from another forum trying to get an answer from a more qualified group - question has come up in the past a few times with no one giving a very good answer)

Muzzle velocity, energy and bullet weight are typically published figures. Many people seem to say bullet weight is most important (maybe suggesting that bullet momentum is the key factor?), others say a high caliber is most important, etc.

After thinking about it for a while I've come up with 2 factors I would think would be most important for immediately destroying a target.

1) Projectile energy
2) Projectile expansion upon hitting target/projectile size

My thinking on these 2 is the projectile will develop high power since

power = (force * distance) / time
where force is force exerted on target by projectile

The projectile expanding on contact with the target would cause in increase in df/dt, resulting in higher peak power (but trailing off more rapidly as due to more rapid loss of velocity).

So since there would be higher peak power, or higher rate of energy transfer, I would think this would be analogous to torching a piece of meat to crisps in a few seconds Vs. heating it in a crock pot for a longer time. Of course that brings the question exactly what sort of damage will that energy cause, if any...

This would lead me to believe that large, light, extremely fast bullets that expand to large sizes rapidly should do the most (immediate) damage...

Can anyone provide insight?

Again, sorry if this is too speculative but there are many myths in this area. It would be nice to know the truth.

Lethality is largely determined by shot placement, penetration, and response time of the local EMS.

However, the goal of most self-defense shootings by law enforcement is not to kill the target, but rather to render the target rapidly incapable of harming innocent parties.

Shot placement and penetration are important for creating incapacitation, but a third ballistic parameter becomes important here: the instantaneous force between bullet and tissue. The force is important because three important wounding effects depend on the force:
1) Prompt damage - a region of tissue destroyed/damaged by the intense stress/pressure field in the region close to the bullet.
2) Temporary cavitation - tissue temporarily displaced by the hydraulic pressure wave radiating outward from the penetrating projectile.
3) Remote pressure wave effects - as the pressure wave radiates outward, it can cause hemorrhaging and remote neural effects that can contribute to incapacitation.

Of course, the force is equal to the local rate of the projectile's kinetic energy loss, dE/dx, so that the impact energy describes the wounding potential of a projectile.

Michael Courtney

 

[mgb_phys]

However, the goal of most self-defense shootings by law enforcement is not to kill the target, but rather to render the target rapidly incapable of harming innocent parties.

Police (or at least specialist firearms units) tend to use hollow point expanding bullets precisely because they do kill - generally police aim is to kill a suspect before they have a chance to kill a hostage, or member of the public.

The military are forbidden by the Geneva+Hague conventions from using bullets that 'cause unnecessary suffering' - the rule was introduced because it is much more effective in a conventional war to injure a soldier so that you tie up resources rescuing and treating them than just to kill someone.
The US ruled that it was allowed to use prohibited bullets in counter-terrorist actions since the other side were not signatories to the Geneva convention. It further allows snipers to use hollow point rounds so long as the intention of them being hollow point is to allow longer range and the fragmentation in the target is only a secondary side-effect.

 

[Dr. Courtney]

Police (or at least specialist firearms units) tend to use hollow point expanding bullets precisely because they do kill - generally police aim is to kill a suspect before they have a chance to kill a hostage, or member of the public.

Unless the CNS is hit directly, most deadly force encounters are over long before the several minutes it takes most shot placements to cause death by loss of blood.

Well placed hits to the chest with service caliber hollow points can create incapacitation relatively quickly (0-10 seconds), and there is great interest and research regarding how to create incapacitation more reliably at the faster end of that range.

The goal of law enforcement training and ammo selection is to rapidly incapacitate their targets. Whether or not violent felons are eventually resuscitated by EMS or succomb to their wounds is beside the point.

Michael Courtney

 

[mgb_phys]

Yes - that was better phrased. I meant to say that the police requirement was to "quickly incapacitate" the bad guy.
I was trying to make the point that the police are definitely not trying to merely wound while soldiers are specifically banned from trying to merely wound.