quote:

Originally posted by ALF:
Posting for Mr. Bekker:

quote:

Denton,

Just a few points to explore:


Question 3:

He goes on to say ...

Shooting the same bullet weight at a lower velocity penetrates deeper?

(What factor is at work here - it does not follow Mo/Xsa optimisation)

The RTD of the animal or test medium.

BigRx

Dimished penetration at higher speeds is a fact. At which point it starts to happen as speed on a particular bullet is increased, depends entirely on how the bullet is constructed and what it's Sd is. As speed rises, stagnation pressure does not increase linearly. It increases as the square of speed. The more frangible the bullet, the quicker the point will be reached where stagnation pressure exceeds the tensile strength of the bullet material and method of construction. When this happens, the bullet expands and the more it expands the more penetration diminishes. (However, there are ways to work around this and take advantage of the forces at work.)

Obviously, factors that reduce penetration are loss of weight and increased frontal area perpendicular to the direction of travel. Projectile shape presented to the direction of travel can improve or reduce penetration.

Bekker,
Ask Saeed how Barnes X bullets work at over 2700 fps versus 2300 fps, and ask him why he prefers the .375/404 velocities instead of .375 H&H when you have the chance.

Yes, I confirm Dr. Ashby's experience. After a certain point, penetration diminishes as impact speed increases. This is true for most, but not all bullets. Premium bullets do better. Monolithic bullets do better than that. The data I have says that monolithics have a very constant penetration depth, over a very wide range of impact speeds. For a 180 grain .308 cal., you get 20" whether it impacts at 3100 fps or 2200 fps.

And the original question I posted caused me to do some more reading. I thought that perhaps simple, non-deforming, cylindrical bullets would probably sweep out equal volumes of wound channel if they have equal impact energies. As you might expect, someone was there long before me, and this is known as Cranz's Law (though I doubt that it is really entitled to anything so lofty as being called a real physical law), and it also assumes an inelastic medium.

Of course, game are not perfectly inelastic, and they have bones and such that make them non-isotropic. Still, if I can understand the simple model, it should help understand the real world, to some extent at least.

I'm thinking that perhaps this penetration phenomonom might partly account for the reputation of such mild rounds as the 6.5x55, and the 7x57, which are reputed to "kill much more effectively than their paper ballistics indicate". With jacketed lead bullets, they get outstanding penetration.

BTW, Gerard, a friend volunteered to give me a box of 243 HV's that he can't use. I'm not quite sure how big a lunch this is going to cost me, but I'm quite excited to test them. They're 67 grainers, IIRC. That seems light for pronghorn, but we'll see. Should get 3500 fps or more out of them.

If we assume the bullet does not deform or turn sideways then I think penetration is determined by the ballistic coefficent of the bullet and its velocity.

In other words the bullet/calibre combination that loses the lowest percentage of its energy from the muzzle to 100 yards will have the geatest penetration.....again, assuming the bullet does not deform or turn sideways.

Of the calibres I have used the one with the greatest penetration has been the old 303 Mark VII ammo which was a very thick jacket and did not breal up like our military 7.62 and 223 ammo FMJs. But somestimes the 303 showed poor penetration when it turned sideways. But I have seen the old 303 Mark VII ammo go through much bigger trees and phone books than would a 375 300 grain Hornady FMJ.

As a side note and a bit off topic....but several years ago, would have been the late 1980s so things might have changed, I had the opportunity to shoot at bank/bullet proof glass. As I remember it was in 5 layers of glass and was about 1.25" thick.

A 223 soft point was stopped easy and you would have has no problem if you were standing with your face right behind the glass. A 308 military was much the same but went in further. A 300 grain Sierra from the 375 was stopped but fragments of glass were blown of the back and you would have had some trouble if were standing right behind the glass, that is, with your face right behind the glass. A 300 FMJ, which if I remember correctly was a Remington factory load....went clean through the glass and also the tree the glass was leaning against and the tree was about 5 inchs in diameter.

We also had some glass that was much cheaper and was about 1 inch thick. It stopped to the 223 but the 308 went through it.

Mike