Different bullets - equal momentum or equal energy?

Factual Questions
21

It has been a long time since I read about DU slugs. The prototypes were produced rather a long time ago, in the seventies, I think. One of the controversial issues was whether what they did constituted a “nuclear weapon” with respect to treaties regarding the use of such things. The defense was that the process that raised the temperature of the uranium was not a self-sustaining one, nor was the result a bomb in the sense described in the treaties under consideration at that time.

Uranium does compress under extremes of force. No, I don’t have a materials text to refer you to, only the understanding that that is why implosive triggers work on fissile materials such as U[sub]235[/sub]. While it does not release sufficient numbers of neutrons easily to create a chain reaction, U[sub]238[/sub] does decay far more rapidly when compressed in the impact with armor at high velocities. That differs markedly with the energy released in a chain reaction fission explosion, but it is still very great, compared to the energy levels of chemical and mechanical interactions. A thousand degrees Celsius is a cool spot in a fission bomb, but in a tank it represents a significant hazard. Chemical processes don’t produce those ranges of temperature.

The DU slugs aren’t hot all the time. They do produce some small amount of heat just sitting around, but not enough to burn anyone. The primary radiation effect is alpha particles, which can be contained within steel-jacketed slugs. The compression of the DU increases the decay rate for a very short time, and then it levels off and stops as the expansion due to heat moves the nuclei further apart. The amount of heat produced is trivial in comparison to a nuclear chain reaction, and inherently self-limiting.

Tris

22

Cool discussion. I like physics and ballistics, but I’m no Einstein or Newton. Not even Fig Newton.

I thought it was neat because of the theoretical aspects of the question. “I assume they will have the same __ at the muzzle”: you meant Muzzle Velocity, I reckon. But I’d think they’d in fact not have the same MV at the muzzle, because one projectile (the DU) is so much heavier and thus more difficult for the charge to move. Downrange, the DU bullet would be more dangerous because of the higher mass/heavier weight. Plasma and all the other esoteric effects aside, the heavier bullet (of equal size) is more dangerous to the target.

Given the choice between being hit by a block of wood and a block of steel of the same size and shape, I’d turn down the steel block. The assumption there is that one is being hit by the blocks moving at the same speed, etc., which becomes less likely with distance. My ex-wife could probably throw the steel block some fair distance, but with a good head start I’d be safe. After all, the steel block ain’t too easy to pitch any distance given the maximum effort that the throw could propel it. She could pitch the wood further with the same level of effort, but since it’s lighter, it’d pack less of a wallop --Kinetic Energy, right?. Given the same pitch energy, the steel block travels less distance than the wooden block but retains more energy at the end of its travel. The thought that the steel block would, because of its mass, be more dangerous to me as long as I was within pitching distance is kind of interesting. Not only does it retain more energy because of its weight/mass, but because it is more dense (weighs more per cubic whatever) than my skull (although my ex might dispute that and for that reason alone want to conduct the experiment), it could penetrate my thick head much more easily that a wooden projectile. I’m sure there’s probably some neato terminal ballistics formula that tell us optimal projectile-to-target densities.

It’s nice to see how these theoretical arguments have their applications in real life.

BTW, I believe during WW II the Germans experimented with anti-tank rounds with cores made of tungsten (which they called “Wolframite”). Like DU, the tungsten was supposed to be so much more dense than the armor of the target that the relationship would be like a hot knife and butter, or perhaps even my ex and I. I reckon they dumped the idea because of the expense and difficulty in getting and working with tungsten.

In my younger days, I worked a little with DU in the form of round disks used as counterweights for aircraft (the Lockheed S-3) control surfaces. As I recall, a piece of DU which was about the size and shape of a coffee can lid felt to be about the same weight as said coffee can when it is full. I still wonder what all might have motivated the designers to use DU when they could have used plastic-coated lead or something similar. Considering the money it cost to get and the expense one had to go to when handling it, they’d literally have been better off using the well known dense metal called “gold”. The main hazard stated at the time was not radioactivity (it’s “depleted” uranium after all, but even depleted batteries have a little spark left), but rather the heavy metal posioning if any fragments or ground-off dusts were ingested. I don’t remember what exactly it was supposed to do, but I do remember that they said you’d get really, really sick. This same aircraft also had brake pads made from beryllium which presented a much greater risk as (I reckon) beryllium is at least as toxic as uranium and is much more like to get at the aircraft mechanics as brake pad dust is part and parcel of brake pads.

23

Tris I’m sure you know tons more about ammo than I do and I appreciate your sincerity and breath of knowledge but I’m really going to need a cite for this to accept it as fact. To imagine that there is some sort of non-mechanical, non-chemical quasi-nuclear but non-fissile self limiting reaction going on when the shell hits the target that generates tremendous heat by accelerating nuclear decay
upon impact in a depleted material is more than I can wrap my head around, also I can’t imagine a substance could work in the manner you described without generating significant and lethal doses of radioactive particles.

I apologize for my ignorance ahead of time.

24

It is one of the more popular threads I have started, so now I shall pat myself on the back. There. I did it.

sailor Actually, the spreadsheet is what I used to come up with the relationship between mass and momentum (holding energy constant). Apparently, the ancients used to use something called a “calculator” to do the same thing, but I’m nowhere near a museum so I had to use what was on my computer. Seriously though, I find that spreadsheets are great because you can see all the mistakes you make and correct them. It’s sort of a “visible calculator” - hey, I should name a product that - visi … calc … doh!

JCHeckler Gold! I’d never thought of that. I wonder if they thought there was too much risk of mechanics pilfering the discs. I’m going to look up some relative densities because I always forgot the densities and remember only the atomic weight.

Here’s a good page on U:
http://www.webelements.com/webelements/elements/text/key/U.html

Densities of the elements under discussion.
Gold density: 19,300 kg per cubic m
Tungsten: 19,250
Uranium: 19,050
Lead: 11,340
Iron: 7874
Aluminium: 2700

So changing from an aluminum ( <- Yank spelling ) bullet to a uranium bullet should increase your momentum by a factor of two and a half (whatever the square root of 7.06 is).

We ROCK!!!

25

If you remove all the fissionable stuff from uranium, you don’t have any uranium left; it’s all fissionable. The U235 and U238 half-lives are 710^8 and 4.510^9 years, respectively, both by alpha decay. Not hugely different. That’s why I don’t know whether Triskadecamus is mistaken. I’d imagine that with enough U238, you could make a bomb, but it might take tons and tons.

26

Ok, i saw this topic, and i had to ask a quetion while we were on the topic.

Since bullets are only affective due to the aerodynamics of them, or something along those lines, what is the principles of a “slug”? I assume you all know what a slug is… It looks like a shotgun sheel, but instead of haveing all those little tiny B.B’s in there, the sheell itself is filled with a rather large, lead, cylinder-like thing.

How does this thing fire? I don;t think a little burst of gun powder would send this thing flying, and if it does, how does it go straight? Shouldn’t it go ricashaying (sorry for the spelling) off somewhere from the air?

just wondering…

27

I suppose technically any element is fissionable. The reason Uranium 235 is extracted from Uranium (leaving behind mostly U238) is that it can form a chain reaction. Get only a few atoms to split and they cause twice as many to split and so on…BOOM!

I think it is possible a cosmic ray (not science fiction ray but real thing) could whip through the earth and split an atom in your desk but that’s about where it would end and you’d probably not even notice.

I suppose upon impact of a high velocity DU bullet a few atoms might split but it would NEVER get critical enough on its own to make a mini-nuclear explosion.

As for radioactivity that’s a product of the Uranium and not nuclear reactions in and of themselves (although the nuclear reaction might convert the isotope into another form of radioactive material). For example, a hydrogen bomb (using the much more powerful fusion reaction instead of fission) is not in and of itself radioactive (hydrogen is not radioactive). The radioactivity comes from the standard A-bomb (using Uranium/Plutonium and fission) wrapped around the hydrogen bomb to make a fusion reaction happen in the first place (fusion reactions are tough to start and require the energy from the a-bomb to start).

In short I don’t think there is any meaningful nuclear process happening when a DU bullet strikes a target. Everything that happens to it can probably be described by straightforward chemical processes.

28

Two things:
Emitting alpha’s is not fission. Fission is when a neutron is absorbed into the nucleus and the nucleus splits into two much smaller molecules. While Uranium and Plutonium can spontaneously fission, it is not reliable enough to use to trigger a weapon, so you have to have a neutron source to get the ball rolling, so to speak. When U-235 fissions it sends out several more neutrons so that more U-235 can fission…which starts the chain reaction. Both U-235 and U-238 can fission, however, U-238 requires fast high energy neutrons, U-235 will fission with about any old neutron, so it is much easier to make it go “bang.”

Second, how does active armour work? I know it works by creating a small plasma ball that screws up the plasma created by the armour-piercer. But how do they set it off? I guess it is a very stable explosive. Does the incoming round set it off, or is there some active sensing system that sets it off?

29

Well, KeithB, I was all set to tell you about how active armor works but it looks like you know just about everything I was going to tell you. The armor is made in cells so you only lose a little bit of armor each time you’re hit by a round; one of the reasons I don’t trust it is, a lot of new anti-tank weapons can hit a tank repeatedly and “hose off” the armor. A case in point is the GAU cannon (7-barrel 30mm) in the A-10.

Anyway, my guess is, there is a relatively stable primer in each armor cell, that won’t be ignited by a rifle bullet or somebody dropping a wrench, but will be ignited by an incoming round. This would be simpler but perhaps less easily “fine-tuned” than a sensing system.

On the subject of shotgun slugs kaos said,

I wish I knew how much powder slugs used, compared to rifle slugs. According to consensus on this board, the amount of powder is roughly proportional to the energy, and shotgun muzzle energies are in the same approximate range as high-powered rifle muzzle energies.

So I expect that slugs use about the same amount of propellant as, say, a .30-06. Of course, the velocities are much lower (between one and two times the speed of sound, compared with Mach 3 for most rifles), but then the slugs are vastly heavier as you’ve mentioned.

There are a couple of ways a slug can be stablized. The first is by using a sabot slug with a rifled barrel - not quite what you’re asking about, since a 12-gauge rifled shotgun is just a .73-caliber rifle.

The other main way to do it is by designing it like a badminton birdie, with a hollow butt and a heavy nose; then you can use it with a smoothbore (a “true shotgun”, at least the way I see it) with reasonable accuracy. Not nearly as accurate as spin-stablization, but much better than a musket ball (which itself would be a lot better than a cylinder tumbling end-over-end).

The third way, which I’ve never seen in an ordinary shotgun, would be to use fin-stabilization like a tank projectile. After all, the main armament of an M1 is a 120mm smoothbore, and they use fin-stabilization. So I suppose it could be applied to a shotgun slug if somebody were willing to put some spring-loaded fins into an object that small…

30

From Depleted Uranium - Vital Stats

"Here’s where the misunderstanding starts. News accounts of “uranium-tipped” shells “burning through” tank armor give the impression that radioactivity gives the DU shells their punch. Not so. Because of its density, DU packs more mass into the same amount of space, thus minimizing air resistance and delivering more kinetic energy, for the same reason a bullet made of lead has greater impact than, for instance, one made of tin. It’s not a different kind of ammunition (as an atomic bomb differs in kind from a conventional one), it’s just a more effective one.

The Defense Department has gone to great lengths to emphasize that these weapons involve traditional kinetic energy, as opposed to any sort of nuclear or radiological energy. This is the interpretation that Peter Jennings seems to have accepted, although it is not entirely accurate. In fact, DU is still radioactive. U-238 is itself radioactive and, even in its depleted state, contains minute traces of the highly fissionable U-235 isotope."

Further down…

" Unfortunately, war is not neat, and this leads to an additional issue that remains still scientifically unsettled. When DU shells explode into enemy armor, and also when they penetrate DU armor in “friendly fire” incidents (which happened on at least one disastrous occasion during the Gulf War), a quantity of the DU burns and oxidizes into minute particles. These particles create an airborne dust that can be inhaled or ingested. In addition to the danger posed by the slight residual radioactivity (i.e., particles lodging in the lungs could eventually lead to cancer), uranium as a heavy metal is quite toxic, and can lead to kidney failure and other health problems. Of course, lead, tungsten and other metals used in armor and armaments are also rather unhealthy to ingest, and they are a major source of wartime health effects"

And…

“Yes, DU is radioactive, but it is not a “nuclear” or “radiological” weapon. No, it is not particularly dangerous in its standard military form; merely being in proximity to DU-armored tanks is unlikely to harm anyone. But exposure to the airborne dust resulting from its use in combat can be harmful.”

Take all of it with a grain of salt because after reading my way through several sites there seems to be several opposing viewpoints with a lot of rhetoric being exchanged.

31

Well, I actually do not know I am just guessing. I thought that maybe they do not even use primer and it takes a lot of energy to get the thing to fire.

It turns out that my cousin is now a county fireman whose area includes Fort Irwin where they do a lot of Battle Simulations. (He says that he does not have much to do since most fireman’s calls are now medical aid emergencies and soldiers are a pretty healthy lot.) Anyway, he is often called out to watch the M1A1’s burning to the ground. His job is to make sure that it does not take anything else with it. I can only guess that either the explosive in the active armour is very stable, or they do not use active armour unless it is possible that it will be needed. I will have to ask next time I see him about this.

32

Slugs aren’t stable over long ranges and some have helical rifling to induce a little spin. They also have a shape that has a little bit of natural stability, similar to a type of low velocity handgun target bullet, a hollow base wadcutter. Oddly the bullets typically used in military rifles and artillery, boat tail spitzer, are aerodynamically unstable. Without the gyroscopic force from spinning the natural flight direction would be blunt end forward.