physics question about bullets

[marine6680]

The problem lies in handgun rounds.


They lack the energy of rifle rounds, energy that can transfer widely into other areas away from the center path of travel.


The energy of a rifle round is better able to rip and tear tissues outside said path, leading to better effectiveness.


Handguns lack this energy, and that means penetration to vitals even at less than optimum shot angles and placement is very important.

 

[s3779m]

I do want to thank all who have written in about energy and the formulas to show how it works. I have learned quite a bit and enjoyed it all. One of these days we should have a thread on something everyone can agree on, like which breed of dog is the best.

 

[mehavey]

...or the right engine oil for vintage British Twins.



.

 

[marine6680]

I quite enjoy these kinds of discussions.

 

[Brian Pfleuger]

Sure you do [care about momentum].... hence the "retained weight" hoopla as you look at

expanded/peeled-back bullets which would otherwise come to a screeching halt before

reaching vitals (like both lungs, or punching through shoulders).



All the kinetic energy in the world is useless if the bullet blows up 3" inside and doesn't have

the momentum to carry it further.



As I said before, this is a systems problem.

That's technically true but I am assuming that the bullet is appropriate for the job. I assume I've picked a reasonable cartridge and a reasonable bullet. At that point, I want KE to expand the bullet, create hydrostatic shock and break things. Most animals, deer, elk, certainly varmints, are pretty easy to penetrate. Momentum isn't really the issue.

 

[mehavey]

If that bullet opens up and presents an expanded diameter, then the momentum behind it is all important.
Otherwise I'd just use 100gr 30 caliber at 3,300fps on elk, instead of 165-180grains at 2,800.

On the other hand a 22 caliber weighing 40 grains doing 4,200fps out of a Swift is just the ticket
for crows. But that same bullet at that same speed blew only a superficial hole in a woodchuck's
gut cavity and exposed his beating heart as he slowly died in front of the 8-year old who shot him.

And that 8-year old never forgot it.

 

[Brian Pfleuger]

As I said... I am assuming proper bullet and cartridge selection.

 

[44flattop]

How long before someone cites "noted forensic pathologist Julian Hatcher" or John Taylor's "knockout formula"?

Are we yet again going to take Taylor's knockout formula out of context? Real easy to sit behind a computer and poke holes at the works of those who actually did something. John Taylor came to his conclusions by killing critters, a lot of them.

Zombie... you are confusing principles and scenarios that are unrelated... so for removed that they are meaningless.

You may get the math and understand the principles... but are not applying them correctly.

Exactly and no one who had actually tested these theories would be coming to these conclusions. Sorry but yet again, for anyone who has actually done the real world testing, it is all too painfully obvious and has been for some time. If all else remains equal, even your precious KE, the heavier bullet will penetrate deeper. Period. End of discussion.

 

[green_MTman]

any bullet with a sectional density of 260 or above can penitrate any big game in north america with reasonable velocity and energy behind it of coarse.

 

[B.L.E.]

I have also killed a lot of critters, and my observation, slow heavy bullets, while they may penetrate, tend to leave relatively survivable wounds and often require follow up shots to get the critter to die. Nothing penetrates like a target arrow considering the KE, but also, nothing leaves a more survivable wound than a target arrow does.

 

[JohnKSa]

Are we yet again going to take Taylor's knockout formula out of context? Real easy to sit behind a computer and poke holes at the works of those who actually did something. John Taylor came to his conclusions by killing critters, a lot of them.

Well said. Whatever else one can say about Taylor's formula (and there is much to be said) it is completely out of context to mention it when discussing shooting humans with handguns as opposed to large African game with heavy caliber rifles.

 

[44flattop]

I've never made a well placed shot with a big bore SWC or LBT that left what I would ever consider a "survivable wound". They won't always incapacitate instantly but they work with boring regularity. Blood trails are short and easy to see.

Well said. Whatever else one can say about Taylor's formula (and there is much to be said) it is completely out of context to mention it when discussing shooting humans with handguns as opposed to large African game with heavy caliber rifles.

Taylor's formula was intended as a way to compare big bore cartridges utilizing heavy, non-expanding bullets to each other. When expanding bullets or high velocity, small bore cartridges come into the mix, it's simply not applicable. The formula places greater importance on diameter and weight. KE places far too much importance on velocity, little on weight and none on diameter. TKO is a valuable tool to compare big bore revolver loads using cast bullets.

It's always interesting when a math/physics nerd thinks he knows better about terminal ballistics.

 

[zombietactics]

If all else remains equal, even your precious KE, the heavier bullet will penetrate deeper. Period. End of discussion.

The problem with that statement is that it is predicated upon an impossibility, i.e. "all else remains equal, even ... KE" ... but somehow we can change mass (or weight) without altering them.

There is no such state of affairs possible in the universe we inhabit.

You cannot have two objects exhibiting all of the same factors: size, shape, velocity, & KE ... but differing only in mass (or weight). It's impossible, as mass, velocity and KE are linked.

Any logic which depends upon the existence of an impossibility is meaningless.

That's just reality. That's the universe we all live in, whether we like it or not, and whether we understand it or not. It's inescapable. A failure to understand this simple truth is a failure to understand this topic at its most elementary level.

Taylor's formula was intended as a way to compare big bore cartridges utilizing heavy, non-expanding bullets to each other. When expanding bullets or high velocity, small bore cartridges come into the mix, it's simply not applicable.

It's not a problem of range or scale. Taylor's formula is nonsense, and does not even repeatably predict the terminal ballistics of rifle cartridges. Every attempt to replicate Taylor's data has failed. That's just a fact.

This article gets it pretty much right: LINK

"... Promotion of this formula is a prime example of the careless way in which a quasi-scientific method is seized upon, even though the originator may reject that purpose to which it is put.

Taylor’s use of bullet diameter, instead of cross sectional area, is in fact mathematically incorrect, as a bullet having twice the diameter to a smaller one has in fact more than twice the cross sectional area. ..."

The last part of that quote is important, as it exhibits clearly that Taylor did not even understand the most basic physical properties involved ... kind of a common thread in this discussion.

It's always interesting when a math/physics nerd thinks he knows better about terminal ballistics.

For the record, I am a test engineer and metrologist, which means I am sort of an expert in how you measure things. I don't simply sit behind a computer all day doing math. Most of the time I have my hands on real things, figuring out how they really work, how to make them work better (or determining why they don't). Call me whatever name you choose, if it makes you feel better. I find it amusing when people who don't understand physics think they understand terminal ballistics (which can be said plainly without stooping to the level of schoolyard name-calling). My participation here is not a matter of chest-puffery or one-upmanship.

Whatever your pet hypothesis is, it cannot operate contrary to the physical laws of the known universe. That's not open to debate, unless we're talking miracles and magic.

 

[Ruger480]

You cannot have two objects exhibiting all of the same factors: size, shape, velocity, & KE ... but differing in mass (or weight). It's impossible, as mass, velocity and KE are linked

In my original question I asked that only velocity and weight be different in order to achieve the same KE numbers.

My hypothetical question was: If you have matching bullets producing the same muzzle energy of say 550ft LBS but one weight 180 grains and the other weighed 155 grains, which one would penetrate further in 10% ballistics gel.

I believe the answer was that the heavier bullet would travel farther.

 

[zombietactics]

^^^^^^^^^^^^^^^^^^^^^^^^^^
Your original question makes perfect sense.

I disagree with the answer given, based upon testing I've done along similar lines.

I'm trying to think of a way to do that experiment, but it's difficult to get "matching bullets producing the same muzzle energy of say 550ft LBS but one weight 180 grains and the other weighed 155 grains" ... or roughly equivalent matching values.

It would also be interesting to test various pairs with the same muzzle energy but differing mass, and plot momentum vs. KE. I am pretty certain you'd see a relationship between KE and penetration far more clearly than momentum. It would be a simple matter of observing that the plotted curve of KE values matches the curve of plotted penetration values, but that momentum does not do so.

This is because we can observe that velocity decreases exponentially over time ... as does KE. Momentum changes in a linear relationship to speed and mass.

 

[JD0x0]

I believe the answer was that the heavier bullet would travel farther.

Assuming same caliber size, then yes. Lighter bullet may be faster, but it loses velocity faster, has less momentum, and a lower sectional density compared to the heavier bullet.
OTOH, if these were bullets of two different caliber. Let's say, the 180 grain is .40 cal and the 155 grain is 6.5mm, the superior sectional density of the smaller diameter bullet would likely allow it to penetrate deeper even though it still would likely have less momentum.

 

[zombietactics]

Assuming same caliber size, then yes

You'd have to assume more than just caliber size ... velocity would have to be identical as well, otherwise you are not controlling for all variables except mass (or weight).

At that point, you have introduced both a difference in momentum and a difference in KE. That's a source of confusion if you don't have a clear sense of what momentum and KE really are, and how they relate to the problem.

A heavier bullet (of a given size/shape), travelling at the same speed as a lighter bullet (same size/shape) will definitely penetrate further. It would exhibit both greater momentum and KE. There is no argument on that point. Physics dictates that result.

OTOH, if these were bullets of two different caliber. Let's say, the 180 grain is .40 cal and the 155 grain is 6.5mm, the superior sectional density of the smaller diameter bullet would likely allow it to penetrate deeper even though it still would likely have less momentum.

I'm not sure the argument for sectional density holds outside the example you've given. For example a 230gr .45ACP handgun round will penetrate quite a bit less than a 55gr 5.56mm rifle round ... even though the .45ACP has both greater sectional density (.162) and momentum than the 5.56mm with a sectional density of .157 and far less momentum. (This assumes you don't get massive fragmentation of the 5.56mm, which will happen in a good number of cases)

 

[45_auto]

A heavier bullet (of a given size/shape), travelling at the same speed as a lighter bullet (same size/shape) will definitely penetrate further. It would exhibit both greater momentum and KE. There is no argument on that point. Physics dictates that result.

I'd be willing to argue that point with you. It's not that simple. There are other considerations besides physics. In real life, you'll find that bullet construction and material make a HUGE difference in penetration.

Just as a simple example, do you really belive that a .30 caliber 168 grain soft point hunting bullet will penetrate further than a 162 grain armor-piercing bullet of the same shape at the same velocity?

To keep it handgun related, we had some Swedish 9mm armor-piercing rounds a few years ago that would easily punch through 3/8" steel plate that any kind of normal pistol ammo would not even scratch.

 

[zombietactics]

... I'd be willing to argue that point with you. It's not that simple. There are other considerations besides physics. In real life, you'll find that bullet construction and material make a HUGE difference in penetration. ...

Adding bullet construction and material would be simply an extension of the factors being considered in a physical model, not a contradiction between "real life" and physics.

If you built accurate physical models of differing bullet constructions, etc. into the problem, you'd get precisely the effects you describe. The Swedish M39 ammo you allude to demonstrates this aptly.

Physics describes the behavior of "real life", in ways which are consistent and allow us to make accurate predictions. It not simply esoteric squiggles on a piece of paper.

 

[44flattop]

It's not a problem of range or scale. Taylor's formula is nonsense, and does not even repeatably predict the terminal ballistics of rifle cartridges. Every attempt to replicate Taylor's data has failed. That's just a fact.

And how many elephants did you kill to come to this conclusion? Your bogus article debunks nothing and it yet another prime example of how the typical idiot takes TKO out of context with the baseball example.

The problem with that statement is that it is predicated upon an impossibility, i.e. "all else remains equal, even ... KE" ... but somehow we can change mass (or weight) without altering them.

There is no such state of affairs possible in the universe we inhabit.

It should be rather obvious to one so astute that for two bullets to have the same shape, same profile, same KE but only differing in mass, they would have to be traveling at different velocities. I'll give you a hint, for two bullets to be identical except for mass, they need to be made of different materials but of similar hardness/toughness. Think copper/bronze and lead.

As has been said, there is too much separation between your education and your experience. Terminal ballistics cannot be explained away through physics and formulas. This is why there is still so much debate. You are way over-simplifying. One would think that if it were this easy to figure out, through the basic laws of physics, that it would've already been done. The issue here is that you simply think your education and occupation, which have nothing to do with ballistics, makes you more enlightened that everyone else. Actually, it's quite the opposite.