Is kinetic energy or momentum a better indicator of bullet penetration?
Well firstly neither pounds nor lb. ft. are even a unit of energy. In empirical the units of energy would be lb. ft^2 / s^2. So I woudn't think the physics analysis of whatever you're reading is worth the glossy paper it is written on. Secondly, there are a lot of factors that effect the effectiveness of a bullet other then their muzzle velocity (shape for one).The reason I ask is because of confusion over various dangerous game hunting articles. In one magazine I read not too long ago, the authour discussed hunting elephant in Africa and stated that, to penetrate the elephant, 4,000 pounds of energy is needed and a minimum rifle such as .375 H&H or .416 Rigby. Another article discussed the ability of a .500 Smith and Wesson magnum or a .454 Casull, both which have between 1,500 and 2,800 lb. ft. of energy, to hunt the same kind of dangerous game (elephant, cape buffalo) effectively. How is this possible?
I take it these gun articles are probably little more than advertisements.Well firstly neither pounds nor lb. ft. are even a unit of energy. In empirical the units of energy would be lb. ft^2 / s^2. So I woudn't think the physics analysis of whatever you're reading is worth the glossy paper it is written on. Secondly, there are a lot of factors that effect the effectiveness of a bullet other then their muzzle velocity (shape for one).
Here is the .375 Holland and Holland Magnum cartridge. For whatever reason, it is considered the standard minimum for hunting cape buffalo and elephant:1. Ft-lbf is a perfectly acceptable unit of energy in the ballistics world. Bear in mind that's pounds force times feet.
2. Let's extrapolate what you need from ballistic standards testing. For standardised vest tests, you find the ballistic limit by finding the bullet velocity at which 50% of the shots will cause penetration. This is found for a specific bullet, meaning it's a combination of mass (hence energy) and geometry (difference between shooting with a spitzer or a ball end round). You could probably penetrate an elephant's skin at the lower bound of the energy ranges stated with a spitzer, but a higher energy for a ball end with the same mass.
Not knowing much about the specific rounds you've mentioned, what's the difference in ogive/ends?
Kinetic energy is converted into momentum as the bullet leaves the gun.Is kinetic energy or momentum a better indicator of bullet penetration?
Kinetic energy is converted into momentum as the bullet leaves the gun.
The Kinetic energy of the bullet leaving the gun is actually resolved into two components
The forward momentum of the low mass bullet and the reaction force of the gun which is the feedback you get.
Now Kinetic energy is defined by the mixture of gunpowder thats present in the gun, but the momentum is defined by the mass of the bullet, like lets say there is some leakage of gun powder at the time of firing the bullet would actually not travel the distance and be less effective.
Ideally all bullets are designed for penetration . So you possibly need to say what kind of penetration u need
Essentially what you are asking is like is the weight of the hammer or the speed of the blow determining the cracking of the nut. They are quite the same products
Right converted is possibly the wrong wordNot to be overly blunt or anything, but that's utter crap. KE and momentum are NEVER 'converted to one another' and they are fundamentally different things.
KE = 0.5MV^2
P = MV
Both KE and momentum are defined by velocity and mass.
Right but isnt it because of the weight that the impact actually cracks the nut?The penetration could be described by either (but is best described by using both), however it needs more detailed description than just a number. The nature of the impact is the important key to both penetration and damage.
Although you have the hammer analogy kind of correct, the thing that actually cracks the nut is force, not momentum or kinetic energy. As force is the mass times acceleration (which is most conveniently found by differentiating mommentum over impact time).
The reason why large slegehammers are used is because, there is generally a maximum swing speed for a hammer and its very difficult to increase it. Yet its very easy to increase mass.
Nope. The closest you'll get is the procedure for finding the ballistic limit for bulletproof vests I mentioned above. There's a big difference between elephants too, so you'd have to find an standardised elephant surrogate for want of a better way of putting it - a thick block of gelatine, covered by a thick leather / aramid skin, backed by a very dense foam.There is a great difference in power between these two cartrdiges, yet both seem to work on elephant. Can a mathematical equation be derived that can show the approximate penetration of a bullet given power and shape?
Thanks for all of the replies! This helps me put everything in better perspective. What I'm still having a hard time understanding is the "rules" for dangerous game hunting which require a heavy calibre rifle with + 4,000 lb. ft.^2 of energy to hunt such heavy game while a comparatively low powered revolver cartridge can equally penetrate through heavy bone and muscle. Is it safe to conclude that these hunting requirements are therefore arbitrary and do not reflect real world requirements?Back the the bullet: To get a true description of the penetration power, both KE and momentum should be used. Along with the geometry of the bullet and the impact.
I don't think that's right. The .454 Casull is currently the reigning champ of handgun carts and it has a max for standard loads of 1923 ft-lbf muzzle energy....the .475 H&H Magnum rifle. It produced 10,000 ft/lbs of muzzle energy....
I see. The mistake I'm making is starting with the premise that you <i>need</i> over 4,000 ft. lbs. of energy to penetrate an elephant or cape buffalo. Do you think a hard cast shotgun slug would do an adequate job as well. What is the rational basis behind laws that require hunters to use a large caliber rifle on dangerous game in Africa, if you know?Damn... I still can't edit.
What I was going to add to my last post is a quote from my 'Cartridges of the World' entry about the .475.
'There is absolutely no need for a cartridge of this power to hunt anything on this planet.'
You got a Magnum Research BFR?I've got a 50-round box of custom .45-70 hand-loads given to me by a couple that loads for BIG handguns. Some each of 405 and 500 gr solid round nose that tach out at over 1800 fps. Now, I need to get lucky enough to win a moose permit in the yearly lottery. Leona LOVES Tom Selleck, and I helped Bill get her a lever-action Winchester that had belonged to him. Bill knew that I hunted with a single-shot Ruger Model 1, and they surprised me with the hot loads as a thank-you. I have put very strong warnings on the plastic box - those loads would blow up a Marlin or Winchester .45-70 and possibly kill the person pulling the trigger.
Nope, and if I did, I certainly wouldn't want to run those hot loads through it. Ouch! My Model 1 can pummel my shoulder with standard 405 gr .45-70 loads if I put enough rounds through it. It's an accurate rifle for target-shooting, though. My first two rounds ever made an elongated hole in the center of the target at 75 yards, using the open sights. My father was looking through my binoculars and said that I missed the paper. I knew that was not the case, so we had to walk up and verify.You got a Magnum Research BFR?
I think that has to do with the bullet being made with a steel core. There are steel core shotgun bullets that will penetrate body armour.I am not certain if it has been discussed here, but the material being penetrated and the density and shape of the bullet are often crucial. For instance, I strongly suspect that a 12 gauge shotgun slug has more kinetic energy than a 5.56 fired by an M-16 or a 7.62 fired by an AK-47; however, both those bullets can penetrate body armor that a shotgun slug cannot.
It also has to do with the shape of the bullet. Full metal jacketed military rifle rounds are designed to concentrate all of the force into a small point, like a shirk, whereas shotgun buckshot spreads the force over a large area and shotgun slugs are generally very rounded instead of pointed.I think that has to do with the bullet being made with a steel core. There are steel core shotgun bullets that will penetrate body armour.