Kinetic Energy = 1/2Mass times Velocity squared

[upptick]

KE=1/2 mv2

I was reading about whether higher velocity hunting rounds have better terminal ballistics and most of the stuff I came across focused on the need for through-and-through penetration of the vitals, causing rapid blood loss in the game animal. But there is also a school of thought out there involving effectiveness being tied to whether the total kinetic energy of the round is transferred to the target, i.e. there is no exit wound. This seems to lead to a discussion of "hydrostatic shock" and whether that phenomenon is real or an unproven hypothesis, the concept being that in addition to mechanical injury there can also be tissue damage caused by a pressure wave if the KE dump is high enough. I do know that years ago I was doing legal work for some surgeons at a hospital in New Orleans and they commented that the military sent their personnel there for training because of the frequency of high velocity rifle wounds, which were regarded as something well beyond the damage caused by typical handguns. I think that was also the reasoning behind the military's adoption of the high velocity 5.56 cartridge in the first place, which seems to be borne out by the empirical data. So, if that's the case, why not just pick the highest velocity round available for a given caliber, optimizing for KE? Or is there a threshold that has to be crossed before hydrostatic shock (i.e. 3000fps?) is possible? I guess this gets into bullet composition, particularly if you're shooting a lower velocity round in the first place. Comments?

 

[mcb]

There are several PhD theses wrapped up in the above paragraph and you would still not be happy with the answers. There is no simple answer to terminal ballistics when it comes to killing biological creatures and their will to live. Seemingly minor wounds result in death and in another case horrific amounts of damage and the individual somehow survives.

With inanimate objects the answers are much much easier. I can simulate in a computer how deep a projectile will penetrate a block of monolith material or even complex materials and the error compared to the real world testing will be low single digit percentages. Trying to predict lethality of a bullet on an animal or person the answers are never clean and concise they are at best general trends and guidelines with lots and lots of exceptions and individual examples both surviving and dyeing that defy the general wisdoms.

IE we can define very precisely how much kinetic energy it will take for a M955 AP projectile to penetrate X amount of a given composition of armor when impacted at an angle of Y. We cannot get anywhere close to that same precision on how much kinetic energy will or will not kill a human shot with that same projectile, there are simply too many variable in the target to concisely track and predict the results of any given hit.

 

[film495]

I've sort of worked through some of this in questions around making up some handloads and what coponents to use. The terminal ballistics do not correlate directly to muzzle nrg. A larger projectile carries more nrg down range - and a lighter one, slows more. So, I'm no expert, but - that is why I think you see self defense ammo - lighter, faster, and hollow point - as the expected use is very short range. For a rifle round, you get into all sorts of questions about how much nrg will be maintained at various distances, drop, and impact of wind on lighter projectiles is also more significant. In my very limited experience, you see heavier rifle bullets used in cartridges for longer ranges, to make them a bit more resistant to wind drift, and to carry more nrg at longer distances - even though out of the gate, the nrg at the muzzle may be lower - but, you're not planning on point blank range targets.

 

[jmr40]

Everything is a compromise. You have to figure out what is the best balance. A round that is highly effective at 100 yards may not be effective at 300 yards where impact velocity is much slower. Then you have to ask, how often are you going to shoot at 300 yards vs inside of 100 yards.

 

[WrongHanded]

So, if that's the case, why not just pick the highest velocity round available for a given caliber, optimizing for KE? Or is there a threshold that has to be crossed before hydrostatic shock (i.e. 3000fps?) is possible? I guess this gets into bullet composition, particularly if you're shooting a lower velocity round in the first place. Comments?

Okay, so according to my (admittedly limited) understanding, it's not the KE that causes the hydrostatic shock, it's the pressure wave from the energy transfer. Meaning that whilst velocity is important, so is the efficiency of the energy transfer. A rapidly expanding bullet will do this more quickly than a FMJ.

But hydrostatic shock isn't everything, and we don't want to rely on it, because animal bodies are complex and squiggly and don't act the way we'd like. We also want mechanical wounding, which means we need penetration and expansion. Sometimes the lightest bullet isn't the best for that.

 

[The Glockodile]

https://www.varmintal.com/

Not trying to be a jerk - but unless one has the insight to look beyond these two limited quantities...

 

[MEHavey]

I am reminded that Energy is a measure of possible destruction capacity, and is very much a function of multiple variables.

Bullet construction:
Velocity upon impact on various surface (and subsurface) objects/organs
Construction of those various objects/organs themselves
Location within the target of those objects/organs
Impact of the destruction of those object/organs

Case#1: Bullet blows up expending all its energy on the skin -- horrific/not-immediately fatal -- long suffering wound/lingering death
Case#2: Bullet "pencils" though -- expending nearly none of its energy -- missing vital organs and causing no hydraulic shock to nearby organs
Case#3: Bullet survives entry -- begins to mushroom to penetrate vital organs -- and leaves trail of destruction as it sheds velocity and energy to stop at rear hide.

All bullets had the same Energy.
But it is a Systems problem, where the variables roll around in a dice cup
(You can load the dice though, if you're smart.)

 

[Rule3]

Will there be a quiz later?

 

[Jim Watson]

There was a strong high velocity is everything school at one time.
In the 1970s I went to the NRA convention and one of the speakers had traveled the world over, shooting various critters with and only with .257 Weatherby 87 gr at 4000 fps. Including big plains game in Africa, I don't recall where he drew the line.
Of course in earlier days that got some intrepid nimrods with .22 Savage Imp, .220 Swift, and even .280 Ross clawed, stepped on, or eaten.

 

[.38 Special]

Overall, I think too much is made of the subject. The search for the laser-flat, bangflop every time, impress all your friends cartridge seems to be uniquely American.

My personal experience is that high velocity is fine if the bullet is up to the task. I really like the .257 Weatherby with all-copper bullets like the TSX. Loading with light weight cup-and-core bullets, though, is asking for trouble and is one of the big reasons why high velocity cartridges still get a bad rap in some quarters: Roy's masterpiece sometimes made for spectacular kills and sometimes for spectacular failures, when the bullets of the time couldn't withstand the velocity.

On the other end is the big and slow crowd, which I more-or-less count myself a part of. Whether we're talking rifles or handguns, a big slow bullet will, in Elmer's words, "make a big hole all the way through, letting lots of air in and lots of blood out". That doesn't always make for lightning kills, but it's reliable and creates a blood trail a blind man could follow. The only downside, at least for some folks, is that big and slow does not make for a long range cartridge. I personally am happy that the fad of taking 500+ yard shots at game animals seems to be fading, but acknowledge that there is a relative handful of hunters who enjoy - and are reliably capable of - such things. For them, a high velocity cartridge is necessary part of the plan.

Otherwise, velocity, energy figures, and the rest are little more than a pastime. We figured out how to reliably kill big game animals with centerfire rifles more than a century ago. Everything after that was little more than marketing.

 

[Engineer1911]

I have made one shot kills (dead right there) on prairie dogs at 150+ yards with a 22 LR, chest shots and dog tips over dead. I have watched prairie dogs "go down the hole" when hit with a 30-06 dragging their entrails. Two of us witnessed a prairie dog flip up in the air, land on its feet, and run about 10' toward its hole. There was a blood spray on the ground where the bullet (25-06 with 75 gr HP bullet) exploded its head. The body was laying 10 feet from the blood spray, where we watched it run towards the hole.