I think you should also consider the bullet's potential of giving its energy to the target. Just compare the soft lead ball of a muzzle loader or a cal. 12 slug to a FMJ-bullet at the same energy.
High speed will give high energy in ², but getting your energy out of mass will give knock-down power (= longer period inside a body so more time to transfert energy).
And now these wise words come into my mind: "A 9 mm might expand, but a .45 will not shrink!"

Either way, you got a dead animal.

The difference is how much meat can you recover?

Stovy, You are looking at it as if Energy and Momentum are the same........ they are not !!!

Go back and re-read Pumpkins first response !!! (excellent response)

Energy is the killing power, it does the work needed. Such as expanding the bullet, making the wound channel, penetrating the intended target, etc. The momentum of a bullet is what will give the intended target a shove, push or knock it down upon impact.

The striking momentum of a bullet can be found with:
M = W * V / 225200
M = striking energy in lb.
W = bullet weight in grains
V = velocity in fps.

168gr bullet
2800 fps

168 * 2800 = 470,000 / 225200 = 2.09

So as you can see the striking momentum with a 168gr bullet impacting at 2800fps is only about 2lbs.

Here is another formula that calculates the shoving effect that a bullets momentum can have on a intended target.

( MB / MT ) * VB = VT

MB = mass of bullet in grains
MT = mass of target in grains (lbs. * 7,000 = grains)
VB = velocity of bullet at range in fps
VT = velocity of target after strike in fps.

So if you were to shoot a 200 lb deer with a 168gr bullet traveling 2600fps upon impact the resulting movement of said target would pretty much be nil.
It would move in the opposite direction at a rate of .312 fps.

168 / (200 * 7,000 = 1,400,000) = 0.00012 * 2600 = .312fps

A 168 grain bullet traveling at 2,800 f.p.s would have about 2,925 ft. lbs. of energy. Not sure how anyone could calculate the ..." the striking momentum with a 168gr bullet impacting at 2800fps is only about 2lbs."... Seems to defy the laws of physics. What am I missing? Take care...
Joe

Lets all keep in mind this thread is about why a deer doesn't fly backwards 30 feet when hit with a bullet carrying over 2000 ft lbs of energy.

Bullet performance is a totally different issue that should only be discussed after stovey's original question is satisfied !!!

chambered221 wrote:

Lets all keep in mind this thread is about why a deer doesn't fly backwards 30 feet when hit with a bullet carrying over 2000 ft lbs of energy. Bullet performance is a totally different issue that should only be discussed after stovey's original question is satisfied !!!

Chambered, go back and re-read stovies OP, he stated that he wanted to know why the shooter wasn't being sent back 30 feet.

Joe, Simply put, kinetic energy does not transfer itself upon the gun or the intended target. If it did the shooter and deer would fly 30 feet backwards.

Ominivision1 wrote:

chambered221 wrote: Lets all keep in mind this thread is about why a deer doesn't fly backwards 30 feet when hit with a bullet carrying over 2000 ft lbs of energy. Bullet performance is a totally different issue that should only be discussed after stovey's original question is satisfied !!! Chambered, go back and re-read stovies OP, he stated that he wanted to know why the shooter wasn't being sent back 30 feet.

yup !!! you right........the deer were blown to smithereens !!! My bad !!!

Ominivision1 wrote:

Chambered, go back and re-read stovies OP, he stated that he wanted to know why the shooter wasn't being sent back 30 feet.

I think pumpkin explained that one...

Also- Chambered made a good point on how the refered to "energy" in "pounds" was a different unit of measure than I think it is.

Interesting responses gents, makes it easier to wrap my head around the "energy" figures.

Happy to help Stovey, I always enjoy discussing shooting related physics. Once again, let me recommend "Understanding Firearm Ballistics" by Robert A. Rinker. Page 342 has a good section in regards to "knockdown".

One more for yah Stovie, taken from a book I have called Handbook of firearms and ballistics by Brian Heard.

Quote:

During the firing of a weapon, the pressure on the inside of the cartridge case acts not only on the base of the bullet, but also on the standing breech of the weapon. It is this mechanism which causes the pistol, rifle or shotgun to recoil.

By knowing the pressure produced (from manufacturers’ published figures)
and the weight of the bullet, the recoil energy can be calculated. For example, the pressure in the chamber of a 0.45′′ calibre self-loading pistol is 14 000 lb per sq. in. The base of a 0.45′′ bullet being 0.159 sq. in., the total pressure on the base of the bullet is 2225 lb, that is, 14 000 × 0.159.

This means that when the pistol is fired, there is a pressure of over 1 ton pushing the bullet forwards and the gun backwards. With a rearward pressure of over 1 ton, the only thing which prevents the gun from being unfireable is that the pressure is only exerted over a fraction of a second.

The duration of this pressure is dependent on the period over which the bullet is still in the barrel. Once the bullet leaves the barrel, there
is no longer any pressure being exerted on its base and therefore no pressure on the base of the cartridge case.

Time of bullet in barrel. It is possible with some fairly simple mathematics to approximate the length of time the bullet will be in the barrel.
If we, once again, take the case of a 0.45′′ calibre self-loading pistol with a
5 in. barrel, with a bullet velocity of 810 ft per second. If the velocity were constant it would exit the muzzle and would give an average speed of 405 ft/s which by the same token gives a time of 0.00102sec. Although this figure is still only partially correct, it does give an
indication as to how long the recoil pressure will be experienced.

UnQuote:

Matt& Bruce Grants book The Sharpshooter has a great sectiopn on recoil. he set up a target to move when hit with a pencil on paper to the side. he shot the target threw a cricket ball at it and set the butt plate against it the amount the target moved was recorded and wasnt alot. find a copy and check it out its a plurry good read and is written by guys who have been there done that in the unique situation we had here in NZ a few years back.

Pumpkinslinger wrote:

Slim, in your example, which one would do the most tissue damage?

I think that would depend on the bullet design. I expect my 405gr laser-cast lead bullets for my .45-70 would not expand but still be sufficient. A modern .45-cal bullet that opens up on impact would be impressive. A .30-cal bullet that expands while retaining its mass is the one I think would do the most tissue damage and provide the deepest penetration. Just an opinion that could spark further debate.

chambered221 wrote:

yup !!! you right........the deer were blown to smithereens !!! My bad !!!