A question of ballistics and physics

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Posted: Sun Oct 25, 2009 9:53 am

In my library is a book titled Crusade In Spain (Faber and Faber, 1974), the memoirs of Jason Gurney, a British sculptor who volunteered to serve against the Fascists in Spain in 1936. It's an excellent book of its type.

In one chapter, Gurney describes a battle with the Fascists and in one pasage he writes about the Fascists using what he calls "high-expansion bullets" (pp. 120-121):

Quote:

In size, the bullet is the same as that used in an ordinary rifle; it has no explosive charge but is, in fact, a super dum-dum. It is formed of a nickel-alloy shell, in the point of which is a small slug of metal with a high coefficient of expansion, the remainder of the shell being filled with lead. The heat set up by the friction of impact causes the inner slug to expand more rapidly than the nickel jacket with the result that the whole thing explodes.

My question to those knowledgeable abouit firearms and/or physics is; does that quotation make sense to you?

Posted: Sun Oct 25, 2009 10:44 am

Without an explosive charge, a bullet is just an inert bit of metal that will never leave the gun.
As far as I know, dum dum bullets expand on impact, not explode.

Posted: Sun Oct 25, 2009 10:57 am

I think he meant with 'no explosive charge' that there is no secondary charge within the bullet that makes it explode inside the target. I have heard of JHP's (jacketed hollow points) that expand to about twice its sice upon impact, but I haven't heard of bullets actually exploding. Wiki article on hollow points

Posted: Sun Oct 25, 2009 11:23 am

Physically it seems possible that the core would expand more rapidly than the jacket. Exploding might in this context mean expanding and changing shape, as a bullet that actually explodes just after leaving the barrel seems barely useful to me...

What you'd need to found out would be:
x Density, Temperature graph of lead
x Density, Temperature graph of nickel
x Increase in temperature of the bullet upon firing

Knowing that the mass of the both the nickel and the lead stays equal when you fire the bullet, you can calculate the new volumes of both lead and nickel when you know the new temperature of the bullet. If the expansion of lead is indeed disproportional to the expansion of nickel, it would be plausible that the bullet's jacket tears open in midair... If that's the case the bullet would probably take on a very unpleasant shape and would then tear flesh on impact in stead of 'cutting' through it.

Disclaimer: I'm no scientific genius, nor do I have any extensive knowledge about firearms/ballistics.

EDIT: Wolframalpha has this to say about thermal expansion:
Lead: thermal expansion | 2.89x10^-5 K^(-1) (rank: 9th)
Nickel: thermal expansion | 1.34x10^-5 K^(-1) (rank: 21st)

I think this says that Lead is the 9th fastest expanding material when you increase the temperature and nickel is the 21s. Looking at the constants in both formula's (the number before 'x10^-5'), I'd say that 'constant' is about twice as high for lead as it is for nickel... Now I'm not sure if that means that lead expands twice as fast as nickel or not, someone with some real knowledge on the subject might want to give his opinion on that, but I do think we can assume that lead does indeed expand faster than nickel.

Posted: Sun Oct 25, 2009 12:30 pm

I always thought the function of an outer jacket was to minimize expansion on impact to make the bullets more "humane".

Baiting Guru Joined: 19 Apr 2007 Posts: 3123

Quote:

bullets more "humane".

Quite a thing to achieve.

Posted: Sun Oct 25, 2009 12:54 pm

@Luckey: It's the Full Metal Jacket bullets that do not expand.

As for the question of how 'humane' bullets are... I don't really see the need to shoot small pieces of metal at each other anyway, but I believe we shouldn't stray into to the fact whether people should be allowed to own guns or not.
Apart from the fact that the expanding bullets would make way nastier wounds than the non-expanding bullets, the expanding bullets still have their advantages, the biggest of which is probably the reduced penetration. With expanding bullets you have less chance of the bullet entering your target, exiting it and then hitting someone else.

Posted: Sun Oct 25, 2009 12:57 pm

^ true, and what also makes it more "humane" is that by creating bigger wounds and doing more damage, the victim/prey goes into shock faster, bleeding faster and thus dieing faster. You know, so they don't suffer that much.

Posted: Sun Oct 25, 2009 1:27 pm

@MTM
The phrase does make sense and as suggested it is not a secondary explosive as such rather the projectile will break up rather than staying in one small ball of lead, the breaking up bit will do loads more damage to any living thing it enters.

"Dum dum" bullets can leave a nice neat entry hole and an exit hole the size of a basket ball.

This effect can be useful when shooting small fury animals, a head shot on a rodent such as a Rabbit using a hollow point projectile will kill the animal instantly every time, even if you do happen to miss its vital organs.

Posted: Sun Oct 25, 2009 3:41 pm

No expert here, Yastreb, but it seems that if the projectile design relied on differing thermal coefficients of expansion to mushroom, the heat gain from the friction of the lands and grooves inside the barrel of the weapon would be at least equal to and probably greater than impact-generated heat; thus the round would expand shortly after leaving the muzzle. This would destroy accuracy, not to mention range.

No, it doesn't make sense.

Hello I'm New here! Joined: 24 Oct 2009 Posts: 5

This definitely seems accurate. Today, they use the hollow-point design instead, but the idea is fragmentation. Impact causes the round to break up upon impact, and the bullet fragments cause more damage than a full metal jacket round.

Simply put, it seams as if the softer part of the round (in the book) pushes up against the hard part of the bullet, which is located at the front. This causes the softer part of the bullet to fragment around the solid portion, and ultimately leads to more damage.

Posted: Sun Oct 25, 2009 4:29 pm

@Ratter: Not only heat gained by friction, it's the heat from the hot gases pushing the bullet out of the barrel as well.

Posted: Sun Oct 25, 2009 4:46 pm

What everyone else has said. Explode as in "to burst violently as a result of pressure from within", not as in "to undergo a rapid chemical or nuclear reaction with the production of noise, heat, and violent expansion of gases".

Murray hit the intent on the head siting the internal damage that is caused after the bullet hits the target.

Posted: Sun Oct 25, 2009 5:31 pm

If I shoot someone, I'm not worried about being "humane" or worried about their injury. I use hollow points in a handgun specifically for stopping power. If someone is attacking me, I want them to STOP. Nothing will stop them better then an exit wound the size of a softball, especially if their heart accompanied the bullet out of that wound.

Posted: Sun Oct 25, 2009 9:59 pm

As wingman said, you want stopping power. It is no use shooting an assailant and the bullet going through that person and injuring someone behind them.

I used to carry hydra shocks as well as Black Talons. Both are hollow point type bullets with a center pin. Typically the entry wound is small but the exit wound is really large. That way you are certain to put a stop to whomever is attacking you.

Black Talon's

Here is a picture of a Hydra Shock in the center. you can clearly see the center pin.

Posted: Sun Oct 25, 2009 10:26 pm

What use is the center pin?

Posted: Sun Oct 25, 2009 11:02 pm

The Hydra Shock design is a combination center pin and serrated jacket. Between the two design features it gives your bullet a much deeper and wider penetration than a regular FMJ. Whereas a FMJ will simply penetrate your target the Hydra shock mushrooms inside producing the signiture exit wound.

The Black Talon in my opinion is worse, the serrations once mushroomed turn into super sharp cutting blades. I may be mistaken but as far as I know they are now banned in mosts states in the U.S.

Wannabe Baiter Joined: 24 Oct 2008 Posts: 80

For fun I have tested this, using a 22 LR. See Rover picture of the 3 shell.
Take a pop can, fill with water
shoot it with a full metal jacket, small hole in, 2 x hole out
shoot it with a normal hollow point, small hole in, 5 x hole out
shoot it with a hollow point that has 5 sides on the inside , small hole in, and the can is in 4 to 5 pieces

Posted: Sun Oct 25, 2009 11:53 pm

I did the same thing with a 2 liter coke bottle full of water. Shot the first one with a regular FMJ nothing exciting happened.

Shot the second one with a hydra shock....... The whole bottle pretty much vaporized in front of my eyes Laughing

The effect of the hydra shock is truly dramatic. I would hate to be on the receiving end of one of those bullets.

Posted: Mon Oct 26, 2009 3:20 am

Wow Rover, I've run the exact "experiment". What I saw was the cap of the plastic bottle fly off about 6 feet. With gallon water bottle, the caps are not screwed on and they only fly about a foot. Hydra shocks turned the bottles into a mist with 9mm Lugers and just a little less mist with 9mm Kurtz. When I saw them going for 1/3 price I immediately cleaned out every WalMart in a twenty mile radius. The best thing about them is that they are a reduced velocity load so they are extremely precise and have a reduced muzzle climb so aimed suppressive fire is possible.

Lead does expand much faster than nickel so the statement does not make any sense. Alloys of lead do behave differently however and each bullet manufacturer has their own composition. I believe that the projective being described must have had a rounded nickel aerodynamic cone with the trailing cylinder of the slug swagged into the lead core. Upon impact, the slug worked like the pin on the Hydra shock, mechanically forcing the slug to deform into one with a greater cross sectional area while flying through the air better than something with a hole in it. I think it was rounded to assist feeding and to ensure sufficient force into the lead behind it upon impact.

Posted: Mon Oct 26, 2009 3:44 am

well, at least I now know something that won't be for sale in Walmart Australia Laughing

did anyone say what the pin does? does it set off the secondary charge or something?

Posted: Mon Oct 26, 2009 5:45 am

It probably forces the viscous material (water in the above examples) outward against the thinner sides of the projectile to create the expansion necessary to turn a small hole into a large hole. A hollow point "fills" and then it expands due to the pressure. The pin would facilitate the "fill" and kind of direct the expansion. Kind of like the prow of a boat directs the water in a direction.

That is just my guess.

Posted: Mon Oct 26, 2009 6:20 am

@ JJJ- The center is for penetration. Hollow point bullets lose penetration power as they mushroom. The hyrda shok design is for maximum penetration plus expansion.

@yasterb - The paragraph makes perfect sense. Only don't think of it as an explosion with fire. That's not what they mean. Think of it as throwing a baseball against a brick wall. The baseball is a normal round. Now throw a coke bottle against the wall. There, you have your explosion.

Posted: Mon Oct 26, 2009 12:12 pm

The bullet would only appear to explode, but it's really breaking up down to the design and the way the energy is being dumped as it hits the target. The bullet jacket breaks up and contents spill out (against of soft target) into whatever it's fired against.

I did a lot of rifle shooting at school, we learned about internal and external ballistics. This is more down to Terminal ballistics which is a bit of a black art. It took quantum mechanics to explain what was going on at the point of impact.

Master of Master Baiters Joined: 26 Sep 2008 Posts: 689

and all it proves is that man has an infinite capacity to kill .... over and over and over.

To me it is a dreadful indictment to see a bunch of grown supposedly civilised humans almost drooling over how lethal and nasty various types of bullets are.

I only found out what FMJ's did when Private Pyle shot himself ... in the head. (!)

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