Simon C

Extreme long shot I know, but I'm trying to explain something to someone and I think it might have relavance to an idea I've had.

Leslie

Maybe it would help if you explained it all.

Les

Simon C

Ok, I'm trying to explain why cavitation and hydrostatic / hydrodynamic (depending on which camp your in) happens.

We know that if you hit an object with a rifle / handgun bullet you get the above effects. Now I'm an archer, so my projectile speeds are alot less than that of firearms, but our arrows weigh in alot more. I've seen the results of animal / arrow encounters, and they look similar, but due to the broad heads cutting action, the effects seem lessened. I'm wondering if speed is the key to the bullets success in the damage.

Edit:

To give you an idea of speeds and wights

.308 is 150 - 185 grn @ about 1250 feet per second

My arrows

500 grn @ 270 fps.

bigsinky

the kinetic energy in a bullet is 5 time that of your arrow. that has to make a difference surely.

CHRIS_D

If this is an arrow vs bullet thread then here is my tuppence.

I would rather have a rifle over a bow and arrow in afghanistan.

That is all.

TonyBurns

iTrader: (3)

A good question Simon
Im trying to get this into my head, its about the blood bubbling?

Well all i can say is that the heat of the bullet may have something to do with it, they get pretty hot at supersonic speeds so do partial cortorisation (think thats right )

Tony

warrenm2

E= 1/2mv^2

Simon C

No its not. its 1 of science.

Simon C

9mm and 45 are usually just below supersonic, but still get the effect, especially .45 ACP.

warrenm2

bullet = 0.5 * 0.16 * 381 ^2 = 11.6kJ
arrow = 0.5 * 0.5 * 82.3^2 = 1.7 KJ

So the bullet has approx 7 times the energy of the arrow - hence more damage (this energy is disapated as a shock wave as well which in itself is more damaging - one of the reasons the US went to high velocity rounds for the Colt I believe - hmmm upon checking it seems it was more to do with being lightweight....)

Danse Macabre

To put it simply, yes, speed is the the main factor.

This is why the faster calibres like .243 and .22-250 are often thought to create more meat damage relative to the diameter of the bullet than heavier but slower rounds like the 6.5x55 swedish.

Hydrostatic shock is basically caused by the inability of the tissue to get out the way fast enough. Consequently, as the fluid cannot compress, the energy is dissipated throughout a wider area around the wound channel.

Another significant factor is that expanding bullets are used in hunting applications and thus the mushrooming and/or fragmentation of the projectile play a part in pushing a large wave front through the tissue.

The effect can be seen in ballistic gel:

JHP = Jacketed hollow point (expanding bullets)
http://www.gunsite.co.za/images/pics...parisonweb.jpg

Bow hunting isn't really my area but I would have thought that another thing to consider is that you are looking to use the energy of the arrow in a slightly different way. With a bullet you are looking for a wound channel with surrounding tissue damage and possibly an exit wound. The damaged tissue then bleeds out behind the bullet and, if it exits, through the exit wound. Consequently you want the tissue to absorb as much energy of the bullet as possible. The perfect scenario is that the bullet passes through, mushrooming out and creating it's wound channel and only JUST pops out the other side, thus delivering all it's energy to the surrounding tissue and leaving two exit holes through which to bleed out.

With your arrow you are looking for it to use it's energy to cut it's own path through the tissue and achieve maximum penetration. As the shaft of the arrow will often be left sticking out the wound channel you therefore want a path wider than the shaft so that blood can pass back past the shaft rather than losing energy by dissipating it into the surrounding tissues as with the bullet.

So basically, your arrow isn't fast enough to create significant hydrostatic shock, and the head doesn't have the correct hydrodynamics to do so. It is designed to create as little drag against the tissue whilst cutting as deep and wide as possible.

Simon 69

9mm certainly isnt subsonic. You can buy subsonic 9mm rounds, but thats not the same thing.

Are you expecting there to be a similarity between a broadheaded arrow and a .308Win travelling at 2,000 miles per hour? My understanding has always been that the bullet pushes soft tissue out of the way in a similar fashion to the air that it travels through, with the cavitation being similar (if you were able to see and compare both).

_Meridian_

iTrader: (1)

9mm is supersonic at the muzzle, Colt ACP is not. However the 9mm slows pretty quickly, and in both cases cavitation is minimal.

The vast majority of the cavitation comes from the supersonic shockwaves, one at the front, one at the rear. There's a very small amount from energy transfer, but only a very small amount. However, bullets can do odd things after they hit: tumble, travel sideways, split, deform, split open etc, all of which will result in wounds that are larger than might be expected. But true cavitation ONLY occurs with supersonic impacts.


M

Midlife......

iTrader: (2)

I thought cavitation in a fluid was caused by areas of low pressure allowing the fluid to make the phase transition to a vapour. Something as slow as a submarine prop can cause this........not wanted as it creates noise LOL

For real impact you need something like an anti-tank Discarded Sabot round at 1200 plus metres / sec

Shaun

Simon C

That makes sense.

Ideally on a bowhunt you would get a complete pass through. This aids blood loss, and subsiquently blood trailing the kill.

Simon C

Cheers all, all thats been said makes perfect sense, a broadhead cuts its way through (irrespective of type, either cut on contact (leaf shaped) or the expandable mechs (blades deploy on contact), a bullet doesn't, it forces its way through.

Who said sensible disscussion was dead on scooby net

Trout

iTrader: (1)

Give me ping Vasily

bigsinky

one ping only

Midlife......

iTrader: (2)

*cough* Red October *cough* LOL

Just to get back on track....I treated a guy who shot himself with a Luger 9mm and the wound track was similar to a knife..

He was cornered by unarmed police (it was a while ago) and decided to end it all so he put the gun under his chin and fired upward !!

the round went behind his lower teeth, through the tongue, behind his nose, in front of the brain, behind the eyes and popped out his forehead (never found) ....missing everything vital .... Lucky guy !

The only thing we had to cut out was the burnt area under the chin !!


Shaun

scrappydoo

Having a background in forensics i believe that it is not just one thing which will cause the great damage when dealing with a bullet as oposed to an arrow. Here are a few things to think about as i will just wheel them off.. It can be as a result of many things, like path of flight, this could include the barraling of the gun which rotates the projectile for stable flight,(arrows when fired loose alot of energy cos they bend and bounce and therefore their distance is impaired), the speed of projectile, friction co-efficients, the impact surface area of the projectile and target, the composition of the said projectile and target. One big factor in damage is the length of flight (distance) as when a bullet is fired, the greater the distance the more the front of the bullet begins to diverge from its centre of gravity. The bullet has such a high pressure wave diffrential on either side that it can literally rip through material hence the large exit wounds, this also plays massively in hydrodynamic cavitation. Also things like atmospheric pressure come into play if you want to get in depth lol.. Anyway im not all that sure cos its been a while and id have to study it to be accurate + there are many other contributing factors which all may be linked in one form or another. This could get very complicated fella. Physics, biology and chemistry combined.

The Trooper 1815

iTrader: (31)

The UK 5.56 mm round will cause more damage than kill. The fact it "tumbles" once inside a different medium (human target) causing damage but not necessarily death will cause injuries to back up the echelon train. Smal entry but a messy internal mass (lead slug tipped with tungsten and a copper jacket) with the round potentially staying in the target. Shorter effective range. Don't forget 5.56mm is not far off .22 inch.

Old 7.62mm rounds killed things pretty well. Small entry, big exit. Messy. Longer effective range.

Simon C

Scrappy doo. A modern arrow in a properly set up bow will be straight after 10 or so yards (not going into it too much here, but its called archers parallax).

Arrows also spin in flight, with straight fletcing, its enough to keep it balanced, with offset or helical, the skys the limit but obviously there is an optimum.

My arrows have about a 2 degree off set which in rilfe terms is probably about 1 in 18 lands.

hodgy0_2

isn't it simply newtons second law of motion F = ma

force = mass X acceleration

so something small in terms of mass but travelling very very fast exerts a powerful force

most army rounds are designed to wound rather than kill outright as the theory goes that it take quite a few enemy soldiers to support lots of wounded soldiers -- so heavy on the enemies logistics

warrenm2

Thats the force to accelerate the bullet out of the barrel. See post 10 for the kinetic energy calcualtion

scrappydoo

ahh now thats interesting, guess bows and arrows are becoming very advanced these days.

archers parallax: is that like a kind of parallax error which is accounted for before firing?

wow this is fasinating stuff. Always wanted to become an archer of some sorts.

ScatRat

iTrader: (7)

i got a jacket de comissioned if you want to play/

Simon C

You can account for AP up to a point before firing, but really its the effect of the string and the bow on the arrow. I'll see if I can dig up some diagrams and an explination.

Technology has moved on vastly in 20 years since I last shot. My arrows are all carbon fibre now, non of this alloy stuff, so vey stiff and light.

The fastest bows produced now, are at 70lb draw weight kicking 350 grn arrows out at 350 fps! 10 years ago that figure was a dream!!!

GarethE

iTrader: (1)

Simon, all this is hypothetical though if you can't hit the target

Gareth

Simon C

I didn't miss thank you



just shot the wrong face

The shot section on this link explains stuff quite well.

OL Adcock Custom ACS Bows

shooter007

bullets also have a vacume that follows behind them low pressure so when it hits an object eg ballistic gell duct seal flesh it pulls air and crap in behind it bullet design can play a large part has as already been said bullet for game are designed to creat a large and so open wound channel this allows the animal to bleed out quickly and suffer less big heavy slow moving round are effective on people as we are not as tough or thick of skin as most wild animals high velocity hand gun rounds eg below normal weight for calibre with large hollow points will dump energy very fast and produce high shock