Penetration & Expansion - Grains or Velocity?

J

J.T.King

New member
Ok...

In a human target, bones and all, what kind of bullet penetrates further? Given the same caliber, will a lighter high velocity bullet penetrate further or will a heavier, lower velocity bullet penetrate further?

Also... Expansion... assuming that the bullet encounters some resitance whether it be barrier or clothing or bone, what type of bullet will expand better after shedding some velocity - lighter faster or heavier slower?

I have read everything on the marshal-sanow page as well as the Dr Fackler stuff (NOTE: I am not trying to start a which is right argument here!), but neither seems to address these two questions.

Thanks for any insight!

J.T.
 
This has got to be the MOST repeated question on every gun BB on the internet.

Get a reloading manual and read it. Then get another and read it. Then another. While you are reading those get a subscription to Shooting Times, Guns & Ammo and Handgunner. Count how many articles address this question. It's never been answered. Except that every one has an opinion and eventually answers it for his/herself.

When all is said and done, heavier and faster is better than smaller and lighter. That's the real answer. You have to decide.
 
Heavy/slow for penetration (hunting) or fast/light for expansion (defense).

One may argue facts, but they are still facts...

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"All my ammo is factory ammo"
 
J.T.King,

I will try to answer you questions based on personal experience with bullet types in hunting situations and data gathered in over 20 years of reloading.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>In a human target, bones and all, what kind of bullet penetrates further? Given the same caliber, will a lighter high velocity bullet penetrate further or will a heavier, lower velocity bullet penetrate further?[/quote]

First, I've never shot a human so I can't comment on that specific target type - but I've hunted deer for a number of years and the body size is similar.

The less a bullet expands the further it penetrates, with all other things being equal. I've fired a .223 FMJ bullet through 7 inches of seasoned oak but a varmint bullet from the same rifle didn't penetrate an inch.

Given the same caliber and bullet construction the heavier bullet will penetrate further, if both are loaded to similar pressures. Given the same caliber it will also be moving slower. The heavier bullet, in the same caliber, has a higher sectional density (same frontal area with more weight behind it). Bullets of different caliber but similar sectional density will usually penetrate the same distance if all other things are equal (velocity, bullet shape, etc)

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Also... Expansion... assuming that the bullet encounters some resitance whether it be barrier or clothing or bone, what type of bullet will expand better after shedding some velocity - lighter faster or heavier slower?[/quote]

Given the same bullet construction (lead alloy, bullet jacket material and thickness etc), and assuming the bullet is properly constructed to expand (hollow point or soft point), the faster bullet will expand more. Velocity is required for reliable expansion. This can be proven with the exact same bullet type loaded to varying velocities. The faster you move it the better it expands.

Hope this answers your questions...

Mikey
 
Thanks guys!

So... let me see if I have this right....

Velocity favors expansion and weight favors penetration.

I understand that everyone has to answer the question of where in that sliding scale the "sweet-spot" is, and I will do that for myself. I think I like the concept of an inbetween kinda thing.. perhaps leaning towards penetration over expansion. Not to say I want a FMJ style bullet, but thats strictly my opinion.

Thanks again!

J.T.
 
So how come...

357 SIG Gold Dot (125/1350): 19/.54 cloth

9mm +P Gold Dot (124/1220): 20/.54

40 S&W 155 GD (155/1175): 18/.57

45 ACP 200 +P GD (200/1050): 18.8/.55

45 ACP 230 GD (230/835): 18.9/.59

Can't make the same old assumptions anymore?

Gotta actually shoot the stuff and see what happens?

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BrokenArrow

Just out of curiosity - what does this data represent (I assume it's bullet weight/velocity: penetration in inches/total expansion?) and what do you think it says with regard to the velocity/expansion assumptions expressed here? Is the data from someone else's tests or yours?

Do you happen to have the sectional density numbers for these rounds. If not, I can calculate them later.

Mikey
 
I'm going to try to address this from what I can remember from physics. Let me list the two catagories: heavy&slow vs. light&fast.

The heavier bullet has more mass, and it can be thought of as a linear representation of torque. The movement "velocity" of the bullet is kind of like the "horsepower".

So when you have a lighter&faster bullet it's generally more useful because it has better expansion, due to the horsepower. BUT, once it hits resistance though, it doesn't have the high torque to "push" it deeper into the subject, thus the penetration. So what's the disadvantage of the heavier&slower bullet? Expansion is a cross product of a the force converted from the Y axis to the X&Z axis, and the basis of that is velocity, and so your displacement force is going to depend on your velocity.

Think of it like this, a bullet like a flywheel. A lighter flywheel is easier to move and can be moved a lot faster, but easier to stop also. A heavier flywheel is harder to move, but on once it's moved, it's harder to stop.

A very light bullet will almost guarantee full expansion, a heavy one will guarantee better penetration.

There are other factors like powder, bullet design, shape, tip type, material etc.. but that's the physics of it. As I remember.

So is a .45ACP superior over say a .357Sig? Depends on what your hunting, how far you want it to penetrate, and how much expansion you would like.

Albert
 
Go here to get the best info on handgun cartridge "effectiveness" on the web:
http://www.firearmstactical.com/wound.htm

Check out the rest of his site. He has some good info:
http://www.firearmstactical.com/tactical.htm

The long and short of it is this: you want penetration from 12 to 16 inches in properly calibrated 20% ordinance gelatin (in both bare gelatin and denim-covered gelatin). If the JHP is designed right it will expand reliably, which is the most you can ask for. Average expansion is then a factor of penetration.

If you want more details, see the sites mentioned above. If you want to know why you can trust tests in 20% calibrated ordinance gelatin to match performance in flesh, which has bones in it, read the book, "Bullet Penetration" by Duncan MacPherson.

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Wound Ballistics is the study of effects on the body produced by penetrating projectiles.
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Some fascinating insights into the current market mania from the Prudent Bear fund.
 
Hello all,

I think Mikey is right on on this matter. Bullet penetration is most closely related to momentum or Mass x Velocity. This has it's limitations also since conservation of momentum assumes an inelastic collision.

Because there of the complicated collisoin I also think kinetic energy(1/2MV^2) has a smaller part due to the stretching of your flesh- therefore storing potential energy.

As stated previously if mass is held constant and velocity increased, there will be an increase in penetration.

Likewise if velocity is constant and the mass (or cross sectional density too) is increased, there will also be an increase in penetration.

Now, for a constant mass and velocity, changes in bullet design matter tremendously- not only for penetration but also for tissue destruction. This in my mind is the real wild card here.

Brokenarrow- I recognize the tables- Firearms tactical right? The differences in penetration have to do with bullet design-IMHO. If one bullet expands 1 inch sooner than the others or tumbles or causes more "nonlaminar" flow of tissues it will penetrate less than the counterparts. Even though the bullet is a "gold dot" are we sure the shape of the nose, diameter of hollow point, etc..... is exacty the same? Not to mention its x-sec & length- this will certainly change the flow characteristics around the bullet.

Simply put the mass and velocity are the 2 boring variables. We can pin those down. The art of modern ballistics is in the bullet design.

Of course I am still awaiting my copy of Duncan Macpherson's book. This is just what I have been able to think of with an engineering degree and a medical background- I am no expert by any means. I can just think of more questions than I can answer.

regards,

Olazul
 
Yep! You can design a light/fast bullet to go deeper than a heavy/slow one. Or a heavy/slow bullet to expand more than a light/fast one. From Firearms Tactical's FBI stuff:

357 SIG GD (125/1370): 16/.60

45 ACP 230 GD (230/847): 13/.74

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From BrokenArrow's first post...

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>357 SIG Gold Dot (125/1350): 19/.54 cloth

45 ACP 230 GD (230/835): 18.9/.59[/quote]

...and from the second

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>357 SIG GD (125/1370): 16/.60

45 ACP 230 GD (230/847): 13/.74[/quote]

You will note in the case of the 357 SIG, an increase of only 20 fps in velocity increased expansion by .04 inches and decreased penetration by 3 inches!

The 45 was even more dramatic - with an increase of only 12 fps in velocity, expansion increased by .15 inches and penetration dropped by 5.9 inches! WOW!!

What better evidence is there for the assumption that increased velocity causes increased expansion and decreased penetration? Speer Gold Dots are finely crafted, controlled expansion bullets (something Speer has done well for a long time). I like this data.

Mikey
 
It will be interesting to see if the introduction of Federal’s EFMJ (Expanding, Full Metal Jacket, I believe) rounds will alter this calculus. While the laws of physics are immutable, new design paradigms can improve performance (i.e., point-of-aim accuracy, penetration and expansion). It is my understanding -- and I am absolutely NOT an expert -- that the EFMJ design’s objectives are to: (1) increase penetration through a FMJ jacket, while (2) ensure reliable and substantial expansion through Federal’s unique bullet “implosion” design.

[This message has been edited by RWK (edited April 01, 2000).]
 
All this technical/theoretical discussion is fun, and interesting. However, if I'm shooting at something that can hurt me, I don't need theory. The round that makes the biggest, deepest hole, i.e. the largest caliber at the highest velocity, is what's called for. I don't care to 'dump all the bullet's energy into the target'. I don't mind making a hole clear through the target and letting air in and body fluids out, while dumping a little excess energy on the hillside or wall or whatever behind it. And I don't mind doing it AGAIN. That's the Law and the Prophets. --slabsides

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If they take our guns, I intend to let my hair grow long and acquire the jawbone of an ass.
 
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