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benEzra
benEzra's Journal
benEzra's Journal
July 18, 2015
Then you should tell all the physicists working on supercavitating projectiles, blades, and foils
that their entire field has been using their terminology wrong since the 1960s and needs to get it straight. Also be sure to tell the peer reviewed fluid dynamics journals that they are doing it wrong and need to revise all their articles ASAP.
But aside from all terminology quibbles, all bullets do form temporary low-pressure cavities in fluid media upon impact, but such cavities are not well correlated with lethality, just temporary incapacitation, and then mostly out of rifle-length barrels. .223 creates such cavities, but smaller ones than deer calibers do, and citing temporary cavity as a rationale for banning centerfire .22's is rather silly, IMO.
July 18, 2015
I think it's really wrongheaded that Marine Corps officers and NCO's
don't have *any* armed response capabilities in off-base situations like this. The best they might manage under the current system is to run to their car where they can legally have a weapon. A civilian desk jockey on a Federal installation sits behind armed protection, but a career officer or master sergeant in a recruiting station or similar facility, even at elevated FPCON, has less ability to defend their installation than my 75-year-old dad does drinking coffee at Bojangles.
It reminds me of post-9/11, when National Guard troops were stationed to "guard" airports and other potential terrorism targets with empty carbines and empty magazines; it doesn't make sense to me, IMO.
July 18, 2015
He wants to ban 100-rounders, he says. Problem is,
the gun control lobby keeps going after popular 11 to 30 round magazines, going back to the 1860s and 1870s, of which there are now a third of a billion or more in U.S. homes.
You guys would have gotten a lot more traction with magazine capacity limits if you set the limit more reasonably, like 30 for rifles and 20 for pistols, instead of aiming for 40% less capacity than a New Yorker could buy in 1862. Calling anything over 10 rounds "high capacity", when the first mainstream civilian repeating rifles of the 1860s held 16+1, most full sized 9mm pistols hold 17+1, and most small-caliber rifles hold 30, is as ludicrous as calling any abortion after 10 weeks "late term". It's simply not. Heck, Lewis and Clark carried a 20-round repeater on their famous expedition in 1804 to 1806, with a power similar to a modern .45 ACP.
Of course, the lobbyists poisoned the well for that issue by going for a 10- or 15-round limit in the first place. After seeing the desired end goal (10? even lower?), even a 30-round limit will likely be seen as only a stepping stone to the ridiculous capacity limits the prohibition lobby wants, and be opposed on that basis.
July 18, 2015
Australia also bans pump shotguns, and is now talking about banning lever-actions
and straight-pull bolt-actions. Australian gun restrictions are ridiculous even by the UK's standards, which in turn are ridiculous by European standards. John Kerry's shotgun would get him tossed into prison in Australia, even though it'd be perfectly legal in the UK.
And calling a non-automatic civilian rifle a "WMD" (especially a relatively low-powered one) is to stretch that term beyond all recognition. If an intermediate-caliber Title 1 civilian carbine is a "WMD", what term do you use for nukes?
July 18, 2015
I would call that "artistic ignorance." (n/t)
July 18, 2015
And that line is drawn at .51 caliber,automatic fire, and explosives.
Non-automatic, non-sound-suppressed handguns, rifles, and shotguns under .51 caliber (with exemptions for some over-.50 weapons, like 12-gauge and 20-gauge shotguns and African big-game rifles) is where the consensus is in this country for gun ownership.
The prohibition lobby has made attacking that consensus its #1 priority since the early 1990s, but the only thing that has done is to discredit the gun control lobby, and hasten the mainstreaming of nontraditional looking civilian guns in the mid-1990s.
Now the guns and magazines the prohibitionists most want to ban define the mainstream, yet are among the least misused weapons in the nation. It's not that the gun control lobby can't grasp that fact, either; they fully understand it, they just don't care.
July 14, 2015
Do you have any *idea* how many American voters
an Australia-style ban and confiscation would affect?
You'd probably be talking in the neighborhood of 60+ million gun owners and 200+ million guns affected, plus a quarter-billion-plus magazines. Even compared to France, Germany, Norway, Finland, and New Zealand, Australian gun laws are downright totalitarian. Heck, they make England's gun laws look relatively free by comparison (Brits can own semiautomatic and pump shotguns with unlimited magazine capacity, whereas Australia even banned and confiscated pump shotguns).
https://en.wikipedia.org/wiki/Gun_laws_in_Australia
July 14, 2015
Either usage is correct, and both are common in the peer reviewed fluid dynamics literature. A cavitating/supercavitating projectile creates a creates a temporary cavity in the fluid medium, not in itself. Yes, cavitating/supercavitating can refer to the fluid flow (especially when considering a system in the rest frame of the solid object, with the surrounding fluid portrayed as moving), but it is also correct to refer to the projectile as cavitating/supercavitating. In both cases, the temporary cavity is created in the fluid medium. For example:
Ditto cavitating/supercavitating hydrofoils:
The usage isn't new, and goes back to at least the 1960s, to the very beginning of computational fluid dynamics. That doesn't mean your use of the term is wrong, either, it's just a different usage, and you see both ways in the fluid dynamics literature.
More broadly, I think your resistance to seeing the temporary cavity as a physics/fluid dynamics phenomenon (and therefore understandable and predictable) stems from the misconception of reading articles and definitions about low-order cavitation (e.g. microscopic cavitation bubbles, small-area sheet cavitation, prop-tip vortex cavitation, pump impeller cavitation, etc. that occur at relatively low Reynolds numbers/high cavitation numbers and are a major engineering headache), and thinking that's all there is to the study of cavitation. Fully developed large-scale cavitation structures, like the attached cavity formed by a bullet in a fluid medium, are described by the same equations and principles; the difference is simply the velocity of the relative flow between the projectile/object and the fluid medium.
The thing is, transition from slow-speed bubble cavitation to fully developed attached-cavity cavitation (where the temporary cavity is much larger than the projectile creating it, as with firearm projectiles) occurs at no more than a few dozen meters per second for a bullet-sized object; any velocity greater than that will produce a fully developed, vapor filled temporary cavity. Since all bullets are traveling between 250 and 1500 meters/sec, they are all waaaaay above the velocity threshold to undergo boundary layer separation and fully developed cavitating flow (e.g. supercavitation) and produce an attached temporary cavity far larger than the projectile itself. In mathematical terms, the cavitation number << the critical value (calculated thusly).
They *do* cavitate---or if you prefer, cause cavitation; either use is acceptable---and it is because of their velocity and the energy they impart to the fluid medium; in a nutshell, they push the medium out of the way so fast that the medium's momentum moves it further than the diameter of the bullet, and it takes a few milliseconds for the displaced fluid to reverse direction and collapse the cavity. The shape and toughness of the bullet determine the shape of the temporary cavity, but the energy of the bullet determines the size.
But here are the more important points that you have gotten away from, with regard to civilian ownership of centerfire .22's:
(1) All bullets produce a temporary cavity, regardless of what you call it.
(2) .223 Remington produces a larger temporary cavity than most handgun bullets.
(3) .223 Remington produces a smaller temporary cavity than most rifle bullets.
(4) Temporary cavity size is not particularly associated with lethality, but at rifle velocities seems to be associated with temporary incapacitation due to transient vascular pressure effects and the body's (presumed) vasodepressor/vasovagal response. Some researchers have argued for temporary incapacitation effects with some handgun rounds also, but the evidence is inconclusive.
(5) Permanent cavity size is highly associated with lethality.
If you fall off a ladder and break a bone, the consequences of the fracture are medical, but Newtonian physics and materials science/engineering tell you how and why the bone broke, can predict the compression/torsion/shear that a particular bone can withstand before breaking, and can tell you what kinds of accidents can generate those forces.
Likewise, if a high speed projectile enters a fluid medium---whether water, ballistic gelatin, or flesh---the consequences of a wound can be medical, and are mostly associated with the permanent cavity. But the impact itself, and the formation of the temporary cavity, are described by high Reynolds number fluid dynamics, not medicine. Temporary cavity is a mathematically describable physical phenomenon, and is determined primarily by the kinetic energy, shape, and deformation of the upset projectile.
Again, you are confusing low-order bubble cavitation (lower Reynolds number, higher cavitation number) with high-order, fully developed attached-cavity boundary layer separation (very high Reynolds number, very low cavitation number). It's still cavitation, but at the high-energy end of the spectrum (aka supercavitation), and you don't seem to be able to grok that they are two ends of the same continuum.
Yes, that's what I'm saying. High speed cavitation involves the formation of attached vapor-filled cavities, e.g. the temporary cavity, not tiny bubbles.
The bullet does indeed create the temporary cavity. Here's a larger-caliber Hornady deer hunting bullet doing just that, in ballistic gelatin:
.223 bullets just happen to create a smaller temporary cavity (and more importantly for hunting, a smaller permanent cavity) than more powerful rifle rounds do, all else being equal.
Well, to get pedantic...
You have strayed a bit from explaining why the least powerful and rarely misused civilian rifles are ZOMG THE MOST DEADLIEST EVAR, but if you want to get pedantic....
You said:
"For something to cavitate is to cause cavitation - to itself. Cavitate is an *intransitive*verb as you are using it, where the verb does not apply to a direct object."
Either usage is correct, and both are common in the peer reviewed fluid dynamics literature. A cavitating/supercavitating projectile creates a creates a temporary cavity in the fluid medium, not in itself. Yes, cavitating/supercavitating can refer to the fluid flow (especially when considering a system in the rest frame of the solid object, with the surrounding fluid portrayed as moving), but it is also correct to refer to the projectile as cavitating/supercavitating. In both cases, the temporary cavity is created in the fluid medium. For example:
Owis FM, Nayfeh AH, "Numerical simulation of 3-D incompressible, multi-phase flows over cavitating projectiles", European Journal of Mechanics - B/Fluids 23:2, Mar-Apr 2004 pp. 339-351 (http://www.sciencedirect.com/science/article/pii/S0997754603001171).
Kulkarni SS, Pratap R, "Studies on the dynamics of a supercavitating projectile", Applied Mathematical Modeling 24:2 (1 Feb 2000), pp. 113-129. (http://www.sciencedirect.com/science/article/pii/S0307904X99000281)
Rand R, Pratap R, Ramani D, Cipolla J, Kirschner I, "Impact Dynamics of a Supercavitating Underwater Projectile". Sacramento, CA: Proceedings of the 1997 ASME Design Engineering Technical Conferences, 1997. (http://www.math.cornell.edu/~rand/randpdf/ahsum.pdf)
Ditto cavitating/supercavitating hydrofoils:
http://www.globalsecurity.org/military/systems/ship/hydrofoil-limits.htm
"In order to prevent damage by cavitation, foils referred to as supercavitating foils have been developed. With a supercavitating foil, a large vapor-filled cavity, referred to as a separation bubble, is formed over substantially the entire upper surface of the foil. Vapor bubbles in the cavity are carried beyond the trailing edge of the foil and collapse in the water aft of the foil, so that shock waves produced by the collapse of the bubbles have much less effect on the foil than in a normal cavitating foil."
Baker ES, Notes On the Design of Two Supercavitating Hydrofoils. Bethesda, MD: Naval Ship Development Center, 1975 (http://www.dtic.mil/dtic/tr/fulltext/u2/a030749.pdf).
The usage isn't new, and goes back to at least the 1960s, to the very beginning of computational fluid dynamics. That doesn't mean your use of the term is wrong, either, it's just a different usage, and you see both ways in the fluid dynamics literature.
More broadly, I think your resistance to seeing the temporary cavity as a physics/fluid dynamics phenomenon (and therefore understandable and predictable) stems from the misconception of reading articles and definitions about low-order cavitation (e.g. microscopic cavitation bubbles, small-area sheet cavitation, prop-tip vortex cavitation, pump impeller cavitation, etc. that occur at relatively low Reynolds numbers/high cavitation numbers and are a major engineering headache), and thinking that's all there is to the study of cavitation. Fully developed large-scale cavitation structures, like the attached cavity formed by a bullet in a fluid medium, are described by the same equations and principles; the difference is simply the velocity of the relative flow between the projectile/object and the fluid medium.
The thing is, transition from slow-speed bubble cavitation to fully developed attached-cavity cavitation (where the temporary cavity is much larger than the projectile creating it, as with firearm projectiles) occurs at no more than a few dozen meters per second for a bullet-sized object; any velocity greater than that will produce a fully developed, vapor filled temporary cavity. Since all bullets are traveling between 250 and 1500 meters/sec, they are all waaaaay above the velocity threshold to undergo boundary layer separation and fully developed cavitating flow (e.g. supercavitation) and produce an attached temporary cavity far larger than the projectile itself. In mathematical terms, the cavitation number << the critical value (calculated thusly).
"Bullets do not cavitate, (unless they are mechanically affected which they cannot in less than a second), they cause cavitation due their mass, velocity, rotation or perhaps tumble."
They *do* cavitate---or if you prefer, cause cavitation; either use is acceptable---and it is because of their velocity and the energy they impart to the fluid medium; in a nutshell, they push the medium out of the way so fast that the medium's momentum moves it further than the diameter of the bullet, and it takes a few milliseconds for the displaced fluid to reverse direction and collapse the cavity. The shape and toughness of the bullet determine the shape of the temporary cavity, but the energy of the bullet determines the size.
But here are the more important points that you have gotten away from, with regard to civilian ownership of centerfire .22's:
(1) All bullets produce a temporary cavity, regardless of what you call it.
(2) .223 Remington produces a larger temporary cavity than most handgun bullets.
(3) .223 Remington produces a smaller temporary cavity than most rifle bullets.
(4) Temporary cavity size is not particularly associated with lethality, but at rifle velocities seems to be associated with temporary incapacitation due to transient vascular pressure effects and the body's (presumed) vasodepressor/vasovagal response. Some researchers have argued for temporary incapacitation effects with some handgun rounds also, but the evidence is inconclusive.
(5) Permanent cavity size is highly associated with lethality.
"There is a diff between cavitation of metallic parts & cavitation used in wound ballistics. The cavitation noted below is NOT what we are concerned with. We are not in an engineering context discussing temporary wound cavities, we are in a medical context."
If you fall off a ladder and break a bone, the consequences of the fracture are medical, but Newtonian physics and materials science/engineering tell you how and why the bone broke, can predict the compression/torsion/shear that a particular bone can withstand before breaking, and can tell you what kinds of accidents can generate those forces.
Likewise, if a high speed projectile enters a fluid medium---whether water, ballistic gelatin, or flesh---the consequences of a wound can be medical, and are mostly associated with the permanent cavity. But the impact itself, and the formation of the temporary cavity, are described by high Reynolds number fluid dynamics, not medicine. Temporary cavity is a mathematically describable physical phenomenon, and is determined primarily by the kinetic energy, shape, and deformation of the upset projectile.
"Cavitation is a significant cause of wear in some engineering contexts. Collapsing voids that implode near to a metal surface cause cyclic stress through repeated implosion. This results in surface fatigue of the metal causing a type of wear also called "cavitation". The most common examples of this kind of wear are to pump impellers, and bends where a sudden change in the direction of liquid occurs. https://en.wikipedia.org/wiki/Cavitation"
Again, you are confusing low-order bubble cavitation (lower Reynolds number, higher cavitation number) with high-order, fully developed attached-cavity boundary layer separation (very high Reynolds number, very low cavitation number). It's still cavitation, but at the high-energy end of the spectrum (aka supercavitation), and you don't seem to be able to grok that they are two ends of the same continuum.
"ezra: due to low-order cavitation and subsequent bubble collapse on the surface of the cavitating object, causing metal fatigue.
jimmy: That is irrelevant to very-high-speed objects like bullets."
Yes, that's what I'm saying. High speed cavitation involves the formation of attached vapor-filled cavities, e.g. the temporary cavity, not tiny bubbles.
"No, the bullet itself does not form any cavity. The cavity formed is the tissue cavitating, not the bullet. As I've said previous, 'cavitate' has morphed into being accepted as you are using it, bullet wise, tho I believe it is invalid usage."
The bullet does indeed create the temporary cavity. Here's a larger-caliber Hornady deer hunting bullet doing just that, in ballistic gelatin:
.223 bullets just happen to create a smaller temporary cavity (and more importantly for hunting, a smaller permanent cavity) than more powerful rifle rounds do, all else being equal.
July 14, 2015
Cavitate is a verb; cavitation is a noun. To cavitate is to cause cavitation, e.g. the formation of a gas filled cavity ("bubble" or "void"
in a fluid medium, in which the local pressure is less than the vapor pressure of the surrounding liquid (which is why cavitation only produces a *temporary* cavity, as opposed to a bubble of gas at ambient pressure). In our context, we are talking about cavitation caused by flow separation around a fast-moving solid object in a fluid medium, and since the cavity is collapsing well behind the object, it is technically supercavitation if you get right down to it.
http://www.merriam-webster.com/dictionary/cavitate
Yes. A fast-moving solid object creating a cavity within a fluid medium is cavitation. Also said of high speed projectiles in water or other dense fluid mediums.The temporary cavity of a rifle bullet is basically textbook supercavitation (the cavity collapses well behind the projectile). Here's a basic primer: https://en.wikipedia.org/wiki/Supercavitation
Thing is, while the displacement caused by cavitation probably does cause some tissue injury, it doesn't appear to be a major contributor to lethality. Temporary cavity may result in temporary incapacitation (perhaps due to vascular reflex), but most wound ballistics experts (such as Fackler et al) point to the size and location of the permanent cavity as the primary predictor of lethality.
A rifle bullet impacts a deer, and a temporary cavity suddenly forms with its apex on the bullet, trailing behind the bullet for a foot or more. Hint: the bullet is the cause of the cavity.
Ummm, no. The cavity a bullet causes is larger than the bullet, and the collapse occurs a foot or more behind the bullet.
Here's a video of a 7.62x39mm round creating a temporary cavity in water, at 27,500 frames per second. Watch the whole thing, and note particularly the temporary cavity formed by flow separation around the cavitating bullet, as opposed to the turbulent bubble formed by the powder. See 2:44 (with temp cavity collapse at 2:51) and 4:44 and following.
FWIW, pitting due to cavitation occurs only in low-grade (non-"super" cavitation, where the cavity is smaller than the solid object creating the cavity, such that the cavity collapse occurs on the object's surface. Over time, constant exposure to low-grade cavitation causes metal fatigue at the surface of the metal, eventually leading to erosion and pitting. That process occurs over hours, weeks, months, or years of cumulative exposure, not in a fraction of a second...and it wouldn't apply to a rifle bullet anyway, because the cavity collapse occurs way behind the bullet, not on the back of the ogive.
Yes, it does. A propeller cavitates when the blade speed through the water is high enough to cause flow separation at that angle of attack. At relatively low blade speeds, it is dependent on blade angle relative to the oncoming flow (e.g. flow separation due to hydrodynamic stall) but at a sufficiently high blade speed it is inevitable. Still, because the blade speed of a boat or ship is relatively low in absolute terms, the cavity collapse often occurs on the surface of the blade itself, leading to metal fatigue and eventual erosion/pitting at the region of constant collapse.
One way around that, of course, is to use a supercavitating prop, designed to spin fast and shaped such that the temporary cavity collapses behind the blade...just like the temporary cavity caused by a bullet in a fluid medium. And bullets are waaaay faster than props, so the collapse occurs further back (go up and look at that video again).
Here is a good representation of a flow field around a bullet in a fluid medium:
[font face="helvetica"][font size="1"]An object (black) encounters a liquid (blue) at high speed. The fluid pressure behind the object is lowered below the vapour pressure of the liquid, forming a bubble of vapour (a cavity) that encompasses the object.[/font][/font]
https://en.wikipedia.org/wiki/Supercavitation
It's also possible to design a bullet of high sectional density and a pointed tip that induces early flow separation, in such a way that it doesn't lose much energy to either hydrodynamic drag or skin friction; the temporary cavity is only large enough for the bullet to fly in. Bullets of that sort don't just brake to a stop in a foot or two of supercavitation, like regular bullets do, but can travel for dozens or hundreds of feet underwater due to their much lower rate of energy loss. That would make for a pretty lousy hunting bullet, though, as the permanent cavity would be very narrow.
Yes, exactly. Bullets (even handgun bullets) travel far too fast for the flow separation cavity to collapse back onto the projectile itself, except for perhaps during the last few mm of travel.
Yes. Your point?
A bullet does not cause flow separation and temporary cavity mechanically? How else do you think it does it?
Temporary cavity is an example of very high speed cavitation (supercavitation) in a fluid medium due to flow separation and the inertial effect of radial fluid displacement. It is a hydrodynamic effect, not a "medical" one, although there may be medical consequences (such as a temporary spike in fluid pressure in the vicinity). The medical consequences of the permanent cavity are what determine lethality, though.
Yep, due to low-order cavitation and subsequent bubble collapse on the surface of the cavitating object, causing metal fatigue. That is irrelevant to very-high-speed objects like bullets.
Flow separation and temporary cavity formation around a high-speed object in a fluid medium is in the realm of fluid dynamics, not medicine. Again, brush up on your fluid dynamics.
For a discussion of cavitation (in the fluid dynamics sense) in the context of wounding from hunting rifle bullets, see this article, under the subheading "II. D. Mechanics of Cavitation".
Yep. Supercavitating props are used on a lot of race boats, and some companies even played with supercavitating hydrofoils for a while. But supercavitation occurs whenever an object moves sufficiently fast in a dense fluid.
Yup. That's because they cause more severe wounds than .223, which is the least powerful rifle cartridge in common use. Larger caliber rifles are also more lethal to humans, though you'd never know it from your rhetoric.
This does go to show just how dishonest the gun control lobby was when it claimed you can't hunt with an AR because it will "blow the deer to smithereens", though. Again, you're trying to make the least powerful rifle cartridges sound ZOMG SUPER SCARY!! compared to more powerful rounds, but the fact is that .223 is less lethal than most rifle rounds. And you have admitted yourself that rifles are the least misused of all firearms....so why the obsession with banning the most popular ones?
Given that we are talking about the least misused guns...
...I think that all this handwaving about centerfire .22's is rather silly. Still, since you bring it up, you might want to brush up on your fluid dynamics a bit.
(Warning: Contains minutiae!)
"I don't agree that 'rifle bullets cavitate, period'. I'm not sure bullets technically cavitate at all. I think the term 'bullets cavitate' has simply morphed into being, similar to how 'incredible' & 'unbelievable' have morphed into different meanings from what they originally meant.
Does a bullet cavitate, or does tissue cavitate? or both?"
Cavitate is a verb; cavitation is a noun. To cavitate is to cause cavitation, e.g. the formation of a gas filled cavity ("bubble" or "void"
in a fluid medium, in which the local pressure is less than the vapor pressure of the surrounding liquid (which is why cavitation only produces a *temporary* cavity, as opposed to a bubble of gas at ambient pressure). In our context, we are talking about cavitation caused by flow separation around a fast-moving solid object in a fluid medium, and since the cavity is collapsing well behind the object, it is technically supercavitation if you get right down to it.
http://www.merriam-webster.com/dictionary/cavitate
"Onelook Dictionary website has 11 dictionary entries for 'cavitate' (mostly irrelevant to this discussion), while it has 25 dictionary entries for 'cavitation', some also irrelevant, but the question is why don't most major dictionaries have a def for 'cavitate' and only for 'cavitation'?
Collins dict: cavitate: to form cavities or bubbles
Merriam Webster: to form cavities or bubbles
wordnik: To form vapour bubbles in a flowing liquid in a region..
Century Dictionary and Cyclopedia To form holes or cavities within an agitated liquid; react upon the water with *cavitation: said of a screw propeller. http://www.onelook.com/?w=cavitate&ls=a"
Yes. A fast-moving solid object creating a cavity within a fluid medium is cavitation. Also said of high speed projectiles in water or other dense fluid mediums.The temporary cavity of a rifle bullet is basically textbook supercavitation (the cavity collapses well behind the projectile). Here's a basic primer: https://en.wikipedia.org/wiki/Supercavitation
Thing is, while the displacement caused by cavitation probably does cause some tissue injury, it doesn't appear to be a major contributor to lethality. Temporary cavity may result in temporary incapacitation (perhaps due to vascular reflex), but most wound ballistics experts (such as Fackler et al) point to the size and location of the permanent cavity as the primary predictor of lethality.
"The above defs mean 'to form' within a structure, or body in our case, I doubt the device used to form the cavity."
A rifle bullet impacts a deer, and a temporary cavity suddenly forms with its apex on the bullet, trailing behind the bullet for a foot or more. Hint: the bullet is the cause of the cavity.
"If a bullet were to cavitate it would become pitted due to collapsing partial vacuums or impingements, irrelevant to this discussion."
Ummm, no. The cavity a bullet causes is larger than the bullet, and the collapse occurs a foot or more behind the bullet.
Here's a video of a 7.62x39mm round creating a temporary cavity in water, at 27,500 frames per second. Watch the whole thing, and note particularly the temporary cavity formed by flow separation around the cavitating bullet, as opposed to the turbulent bubble formed by the powder. See 2:44 (with temp cavity collapse at 2:51) and 4:44 and following.
FWIW, pitting due to cavitation occurs only in low-grade (non-"super"
cavitation, where the cavity is smaller than the solid object creating the cavity, such that the cavity collapse occurs on the object's surface. Over time, constant exposure to low-grade cavitation causes metal fatigue at the surface of the metal, eventually leading to erosion and pitting. That process occurs over hours, weeks, months, or years of cumulative exposure, not in a fraction of a second...and it wouldn't apply to a rifle bullet anyway, because the cavity collapse occurs way behind the bullet, not on the back of the ogive.
"In an alternative definition of 'cavitate', a screw propeller will cavitate at, generally, higher ship speeds full or flank, but it does so over minutes, hours, days, months in the water. A bullet can pass thru a soft target in a fraction of a second, does it truly 'cavitate' when it truly cannot?"
Yes, it does. A propeller cavitates when the blade speed through the water is high enough to cause flow separation at that angle of attack. At relatively low blade speeds, it is dependent on blade angle relative to the oncoming flow (e.g. flow separation due to hydrodynamic stall) but at a sufficiently high blade speed it is inevitable. Still, because the blade speed of a boat or ship is relatively low in absolute terms, the cavity collapse often occurs on the surface of the blade itself, leading to metal fatigue and eventual erosion/pitting at the region of constant collapse.
One way around that, of course, is to use a supercavitating prop, designed to spin fast and shaped such that the temporary cavity collapses behind the blade...just like the temporary cavity caused by a bullet in a fluid medium. And bullets are waaaay faster than props, so the collapse occurs further back (go up and look at that video again).
Here is a good representation of a flow field around a bullet in a fluid medium:
[font face="helvetica"][font size="1"]An object (black) encounters a liquid (blue) at high speed. The fluid pressure behind the object is lowered below the vapour pressure of the liquid, forming a bubble of vapour (a cavity) that encompasses the object.[/font][/font]
https://en.wikipedia.org/wiki/Supercavitation
It's also possible to design a bullet of high sectional density and a pointed tip that induces early flow separation, in such a way that it doesn't lose much energy to either hydrodynamic drag or skin friction; the temporary cavity is only large enough for the bullet to fly in. Bullets of that sort don't just brake to a stop in a foot or two of supercavitation, like regular bullets do, but can travel for dozens or hundreds of feet underwater due to their much lower rate of energy loss. That would make for a pretty lousy hunting bullet, though, as the permanent cavity would be very narrow.
"any cavitation bullet creates does not affect it whatsoever, since it is long gone by the time the temporary wound cavity collapses. "
Yes, exactly. Bullets (even handgun bullets) travel far too fast for the flow separation cavity to collapse back onto the projectile itself, except for perhaps during the last few mm of travel.
"If bullet hits bone or does not exit, collapsing tissue on the back end has no relevant affect on a bullet, it's a one trick pony & does not get shot again."
Yes. Your point?
"This is actually not what is meant when referring to a bullet however, since bullet wise we are speaking of 'medical related' cavitation, not mechanically affected cavitation."
A bullet does not cause flow separation and temporary cavity mechanically? How else do you think it does it?
Temporary cavity is an example of very high speed cavitation (supercavitation) in a fluid medium due to flow separation and the inertial effect of radial fluid displacement. It is a hydrodynamic effect, not a "medical" one, although there may be medical consequences (such as a temporary spike in fluid pressure in the vicinity). The medical consequences of the permanent cavity are what determine lethality, though.
"'your-boat-guy' website, how a propeller cavitates in the bubbly sense: Many propellers partially cavitate during normal operation, but excessive cavitation can result in metal erosion or "cavitation burn" to the prop's blade surface."
Yep, due to low-order cavitation and subsequent bubble collapse on the surface of the cavitating object, causing metal fatigue. That is irrelevant to very-high-speed objects like bullets.
"cav·i·tate To form cavities in an organ or tissue .. cavitate formation of cavities.
cav·i·ta·tion 2. the formation of cavities, esp in a part of the body. 3. Medicine The formation of cavities in a body tissue or an organ, especially those formed in the lung as a result of tuberculosis. http://www.thefreedictionary.com/cavitate"
Flow separation and temporary cavity formation around a high-speed object in a fluid medium is in the realm of fluid dynamics, not medicine. Again, brush up on your fluid dynamics.
For a discussion of cavitation (in the fluid dynamics sense) in the context of wounding from hunting rifle bullets, see this article, under the subheading "II. D. Mechanics of Cavitation".
"new to me, super cavitation: A propeller is said to be fully cavitating when the whole of the back is covered in sheet cavitation. This phenomenon is also called super cavitation.. "
Yep. Supercavitating props are used on a lot of race boats, and some companies even played with supercavitating hydrofoils for a while. But supercavitation occurs whenever an object moves sufficiently fast in a dense fluid.
"Most larger caliber rifle-hunting bullets (i.e, larger than .223 --bE) are more likely to cause a quicker death to the animal, too."
Yup. That's because they cause more severe wounds than .223, which is the least powerful rifle cartridge in common use. Larger caliber rifles are also more lethal to humans, though you'd never know it from your rhetoric.
This does go to show just how dishonest the gun control lobby was when it claimed you can't hunt with an AR because it will "blow the deer to smithereens", though. Again, you're trying to make the least powerful rifle cartridges sound ZOMG SUPER SCARY!! compared to more powerful rounds, but the fact is that .223 is less lethal than most rifle rounds. And you have admitted yourself that rifles are the least misused of all firearms....so why the obsession with banning the most popular ones?
July 10, 2015
There is no "if cavitation occurs"; rifle bullets cavitate, period, and most larger calibers cause more cavitation than .223 does, since the volume of the temporary cavity is roughly proportional to the energy transferred.
A fragile, light-for-caliber bullet at 3000 to 4250 ft/sec (40 or 55gr .223 JHP, 55gr .22-250, 58gr .243, 90gr .270, 55gr .30-06) will produce a much shorter, but wider, wound track than a limited-expansion, bonded-core bullet (like .223 50gr Barnes TSX, 60gr Nosler Partition, 62gr Remington Core-Lokt) or heavy-for-caliber bullets (77gr bonded core .223, 110gr .243, 140gr .270., 180gr .30-06). But the temporary cavity size is still proportional to the energy.
For killing a large game animal humanely, the wound has to be deep enough to reach the vital organs after penetrating the shoulder. A .223 can create a deep cavity with a bonded core hunting bullet, but it's not very wide, and hence requires very precise shot placement. For example, a Nosler 60gr .223 deer hunting bullet penetrates 18.5" and doesn't fragment, but the permanent cavity is less than half an inch across, requiring a much more precise shot than you would need with a bonded core 130gr .270 traveling 300+ ft/sec faster.
http://www.midwayusa.com/product/862243/hornady-superformance-sst-ammunition-270-winchester-130-grain-sst-box-of-20
Yes, exactly. And for all bullet styles, rifles like .243, .25-06, .270, and .30-06 produce more cavitation and more severe wounds than .223 does, whether you are comparing light-and-fragile .223 to light-and-fragile .25-06/etc., or tough bonded-core .223 bullets to bonded-core .25-06/etc. .223 is the least powerful rifle caliber in common use, and it shows.
Choosing a fragmenting .223 bullet instead of a bonded core .223 for hunting small deer would be as stupid as choosing birdshot over buckshot for the same purpose. Fragmenting bullets are for small game and to limit penetration at in-home distances, not for shooting deer. .223 deer loads would be the NON-fragmenting bonded core rounds, like Nosler Partition, Barnes TSX, Remington Core-Lokt, etc., which typically give 18" or so of penetration and no fragmention.
The exact same scenario of a shallowly wounded animal running off would occur if an idiot hunter were shooting fragile loads out of a .243, .270, or .30-06 (or 12ga birdshot, for that matter). A 58gr .243 doesn't penetrate any more than a 55gr .223 does, it just fragments more violently and makes a wider wound.
Limiting the discussion to modern rifle cartridges, fragmentation isn't a function of caliber at all; it's a function of bullet construction primarily, and velocity secondarily (which in turn depends on the bullet weight chosen within that caliber). A 58gr .243 will fragment more violently than a 55gr .223, more in line with a 40gr .223, even though .243 is a respected deer caliber.
Yes, absolutely. Common handgun velocities are in the range of 850 to 1500 ft/sec, primarily due to the short barrel length (making high powder capacity superfluous). There is some question about whether temporary cavity can affect some tissues above 1100-1200 ft/sec (e.g., +P 9mm at 1300+ ft/sec, or 125gr .357 Magnum at 1600 ft/sec) but at the 2600-4300 ft/sec velocities of hunting rifles, temporary cavity can be a big deal.
What you're missing is that if either temporary cavity size and fragmentation, or velocity, are your criteria for banning rifle calibers, then .223 would be waaaay down the list. You seem hung up on .223 FMJ or light JHP, but go look up the ballistics of .22-250, or .243/.25-06/.270/.308/.30-06 with the light bullets, and get back to me. The little .223 is a rifle round, but its lack of power shows when you compare its terminal ballistics to other common rifle calibers.
Thoughts...
Here's what you said:
"If cavitation occurs the animal can wander off & be in unbearable pain for days, moreso than with other hunting bullets."
There is no "if cavitation occurs"; rifle bullets cavitate, period, and most larger calibers cause more cavitation than .223 does, since the volume of the temporary cavity is roughly proportional to the energy transferred.
A fragile, light-for-caliber bullet at 3000 to 4250 ft/sec (40 or 55gr .223 JHP, 55gr .22-250, 58gr .243, 90gr .270, 55gr .30-06) will produce a much shorter, but wider, wound track than a limited-expansion, bonded-core bullet (like .223 50gr Barnes TSX, 60gr Nosler Partition, 62gr Remington Core-Lokt) or heavy-for-caliber bullets (77gr bonded core .223, 110gr .243, 140gr .270., 180gr .30-06). But the temporary cavity size is still proportional to the energy.
For killing a large game animal humanely, the wound has to be deep enough to reach the vital organs after penetrating the shoulder. A .223 can create a deep cavity with a bonded core hunting bullet, but it's not very wide, and hence requires very precise shot placement. For example, a Nosler 60gr .223 deer hunting bullet penetrates 18.5" and doesn't fragment, but the permanent cavity is less than half an inch across, requiring a much more precise shot than you would need with a bonded core 130gr .270 traveling 300+ ft/sec faster.
http://www.midwayusa.com/product/862243/hornady-superformance-sst-ammunition-270-winchester-130-grain-sst-box-of-20
"it's the degree of cavitating expansion which causes the damage, moreso to surrounding internal organs. Handgun bullets below ~1,000 fps (iirc) generally don't cause significant cavitation, their wounds are often considered akin to being stuck by a dagger or run thru by a thin fencing foil (sword) - the permanent wound cavity."
Yes, exactly. And for all bullet styles, rifles like .243, .25-06, .270, and .30-06 produce more cavitation and more severe wounds than .223 does, whether you are comparing light-and-fragile .223 to light-and-fragile .25-06/etc., or tough bonded-core .223 bullets to bonded-core .25-06/etc. .223 is the least powerful rifle caliber in common use, and it shows.
"After fragmenting, the .223 inside an animal could result in two separate temporary cavities, just like in a human, but greater likelihood than larger hunting rifles for the .223 wound NOT to be fatal, thus resulting in the animal running off mortally wounded & in great suffering."
Choosing a fragmenting .223 bullet instead of a bonded core .223 for hunting small deer would be as stupid as choosing birdshot over buckshot for the same purpose. Fragmenting bullets are for small game and to limit penetration at in-home distances, not for shooting deer. .223 deer loads would be the NON-fragmenting bonded core rounds, like Nosler Partition, Barnes TSX, Remington Core-Lokt, etc., which typically give 18" or so of penetration and no fragmention.
The exact same scenario of a shallowly wounded animal running off would occur if an idiot hunter were shooting fragile loads out of a .243, .270, or .30-06 (or 12ga birdshot, for that matter). A 58gr .243 doesn't penetrate any more than a 55gr .223 does, it just fragments more violently and makes a wider wound.
"Well aware that bullet characteristics are finicky, and that fragmentation is not solely a function of caliber."
Limiting the discussion to modern rifle cartridges, fragmentation isn't a function of caliber at all; it's a function of bullet construction primarily, and velocity secondarily (which in turn depends on the bullet weight chosen within that caliber). A 58gr .243 will fragment more violently than a 55gr .223, more in line with a 40gr .223, even though .243 is a respected deer caliber.
"wiki, eh; most all of this you will concur, but it backs me up: Most handgun projectiles wound primarily through the size of the hole they produce. This hole is known as a permanent cavity. For comparison, rifles wound through temporary cavitation as well as permanent cavitation. A temporary cavity is also known as a stretch cavity. This is because it acts to stretch the permanent cavity, increasing the wounding potential. The potential for wounding via temporary cavity depends on the elasticity of the tissue, bullet fragmentation, and the rate of energy transfer.
Many handgun bullets do not create significant wounding via temporary cavitation, but the potential is there if the bullet fragments, strikes inelastic tissue (liver, spleen, kidneys, CNS), or if the bullet transfers over 500 ft·lbf (680 J) of energy per foot of penetration."
Yes, absolutely. Common handgun velocities are in the range of 850 to 1500 ft/sec, primarily due to the short barrel length (making high powder capacity superfluous). There is some question about whether temporary cavity can affect some tissues above 1100-1200 ft/sec (e.g., +P 9mm at 1300+ ft/sec, or 125gr .357 Magnum at 1600 ft/sec) but at the 2600-4300 ft/sec velocities of hunting rifles, temporary cavity can be a big deal.
What you're missing is that if either temporary cavity size and fragmentation, or velocity, are your criteria for banning rifle calibers, then .223 would be waaaay down the list. You seem hung up on .223 FMJ or light JHP, but go look up the ballistics of .22-250, or .243/.25-06/.270/.308/.30-06 with the light bullets, and get back to me. The little .223 is a rifle round, but its lack of power shows when you compare its terminal ballistics to other common rifle calibers.
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