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There's way more factors. I don't think you can get to "all else being equal" given just the factors you've listed. Bullet construction is going to play a large part, for example (consider the shooting of a bullet designed for a 30-30 in a 300 mag/ultramag). Propensity to tumble is another. Type of biological tissue is yet another. Part of what you want is sectional density (weight/diameter^2). This concept combines 2 of your above factors in one term. It says a lot about penetration, but little about actual bullet performance in contact gelatinous or calcified materials at various velocities. My best guess is that in a laboratory, in standardized gelatin blocks, with fmj bullets, at stabilized spin rates, at equal velocities, bullets with higher sectional densities would penetrate further than equivalent weight/caliber bullets with lower sectional densities. And, in the same setup, except fixing sectional density and varying velocity, penetration would depend on velocity. Finally increasing both would likely multiplicatively increase penetration. But in going to this extreme, we've thrown out a whole lot that is of practical value to a hunter. | |||
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Penetration is a direct function of Momentum Velocity x Mass. The force applied by the bullet is inverse to it's cross section (force /area = pressure). Sectional density is how much mass is behind the crosssection oif the bullet. For any given caliber it varies as the bullet length. So far a small caliber heavy bullet at high velocity will penetrate furthur. Where the problems come in to this neat picture occurs during bullet expansion where a lot of things happen at once. Basically penetration depends on momentum, and wound cavity depends on bullet energy. Good luck! | |||
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# 1 Bullet construction... obviously a 500 gr .458 made of compressed powdered lead will NOT penetrate as far as a 400 gr .458 barnes solid. #2 Physical (constant) properties of the bullet. Caliber, Mass, and #1 above. Since caliber and mass, of a given contruction, determine SD and Cross SD, every other than velocity is a SECONDARY artifact. #3 velocity... there is a window that will penetrate well for a GIVEN bullet... Of course, this is all thrown out the window if you are using a carcano!! Momentum, precisely like Muzzle Energy and Taylor knock out values (what's the Momentum of a 12 ga slug vs an Arrow) are all shorthand definitions of an instant snap shot of the energy in the system. All these values also bleed down, radically, with velocity. jeffe opinions vary band of bubbas and STC hunting Club Information on Ammoguide about the416AR, 458AR, 470AR, 500AR What is an AR round? Case Drawings 416-458-470AR and 500AR. 476AR, http://www.weaponsmith.com | |||
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I agree with this. Take two bullets of the same SD and velocity, vary the calibers and they "should" penitrate the same. The problem is when they start deforming, they spend energy on destroying them-selfs and not on penitration. The reason some claim bullets penitrate best at medium velocity is the bullet holds together better and isn`t wasting energy deforming and in effect changing its SD as it does when stressed at max vel. ------------------------------------ The trouble with the Internet is that it's replacing masturbation as a leisure activity. ~Patrick Murray "Why shouldn`t truth be stranger then fiction? Fiction after all has to make sense." (Samual Clemens) "Saepe errans, numquam dubitans --Frequently in error, never in doubt". | |||
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Bullets do some very counterintuitive things. Many bullets penetrate less at higher speeds. The higher speed impact apparently opens them up farther, and they shed more weight, so they penetrate less. In soggy phone books, Hornady Interlocks and Speer Spitzers tend to penetrate about 10-11 inches at 3100 fps, and more like 14-15 inches at 2500. I've got some independently taken data that says the monometals tend to produce practically the same length wound channel, over a very wide range of impact speeds. The experiment showed 18-22 inches, from 2200-3100 fps. A 180 grain conventional bullet, at the highest speed you can get out of an '06, will penetrate farther than a 150, at the highest speed you can get out of it. Prove all things; hold fast to that which is good. | |||
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For bullets of equal construction, its sectional density times velocity. However, the velocity variable is actually a curve that prevents penetration from increasing proportionately as velocity increases. | |||
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Alf, We have to stick to nondeforming solids first. Expanding bullets will complicate the basics. Also assume the perfect nose profile, whatever that is, but nondeforming. Then, purely momentum predicts the penetration for a given caliber. Mass and velocity are interchangeable. A certain amount of mass is best to get adequate momentum, given the restraints of velocities possible within pressure limits. It gets harder to get momentum up with ever lighter bullets without pressures going through the roof in our usual sporting rifles. This mitigates for heavier bullets. However, longer heavy bullets will be less stable and more prone to bend in the real world, within common twist rates and bullet materials being what they are. This mitigates against heavier bullets. So there is a happy balance where you get a certain weight for caliber that maximizes both momentum and stability. Too much weight is bad, and too little weight is bad. When you get the right weight and the bullet is tough enough, then the more velocity, the better. This is the absolute, fundamental truth. | |||
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Of two similarly constructed bullets, fired from the same rifle, and on the same medium, the one with a greater sectional density will out-penetrate the other. | |||
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Ray, Not so easy. You did not say what velocities those bullets of different sectional density were traveling. Your answer is negligently incomplete. | |||
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Penetration is too complex to define with one number or analogy. It is a function of energy, momentum, bullet shape (cross sectional area and shape), and construction. Energy is the ability to do work, or in this case penetrate tissue. If everything else is equal more energy gives more pentration. Momentum affects how quickly a bullet loses its energy. A bullet with a high amount of momentum will slow down more gradually than a bullet with less momentum. If everything else is equal more momentum will give increased pentration. A small fast bullet with enrgy equal to a large slow bullet will lose its velocity quicker in a ballistic gelatin. Quick velocity loss (or energy transferred to the target) creates a large wound channel with a short length. Slow velocity loss creates a longer, narrower channel in the gelatin. The volume of tissue destroyed will be approximately the same (theoretically), if everything else is constant. The shape of the bullet affects penetration in two ways. A sharply pointed bullet has less area and for a given amount of force creates higher stress in a medium. In general terms it's easier to pound a sharp nail (small x-sect) into a board than a ball bearing (large x-sect) with the same mass. The cross section area also influences it. It's easier to drive a small nail into a board than a railroad spike. Bullet construction affects penetration in the same way. A heavily constructed bullet loses its energy slower than a lightly constructed bullet. In general at the same energy level a tough bullet will produce a longer narrower wound channel. A lightly constructed bullet will create a short wide wound channel. The trick that ballistics engineers try to accomplish is to get the area of the tissue destruction to be greatest in the vital organs of a typical game animal. This is usually accomplished by have a bullet that makes a small entry hole and as it deformsit gets bigger and bigger in the center of the chest cavity. As it loses energy the wound channel will narrow down again and the bullet will just penetrate the far side of the chest, expending all its available energy (or creating the most tissue destruction) inside the animal. There is not a linear realtionship here that you can definately say bullet X will outpenetrate all the others based on these calculations. each of the factors affects the others. If you have more momentum you may need a more lightly constructed bullet to work well. If you increase velocity (energy) you may need a tougher bullet. Ballistics engineers use the factors I listed to make an edjucated guees about what bullet design for a given caliber, at an assumed velocity (based on the most common firearms in that caliber), shot at an animal of an onknown weight and toughness, will work best. Then they test them extensively, and make small adjustments to get the best result. If they could define what would pentrate best based on one mathematical equation there would be no need for them to do extensive (and expensive) testing. | |||
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Not so fast Gerard! Please make a comment about the solid bullet with no deformation and an ideal nose profile, whatever that may be. Sure, if you have a hollowpoint or soft nose, then increasing velocity at some point will result in a fall off of penetration, becasue the bullet over expands/blows up/ loses to much weight/increases drag with XSA increase/tumbles, etc. I believe Alf's question is a hypothetical one involving only mass, velocity, and caliber. No deforming bullets can be considered until the basics are put to rest with a solid bullet. Then it gets complicated. Either short disk like bullets or too long bullets are no good. There is an ideal penetrator weight in there somewhere, and it is not the bullet with the highest "SD." | |||
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"All else being equal", (which it never is!!), a slow, heavy bullet penetrates better than a light, fast one ASSUMING THE SLOW HEAVY ONE HAS A GREATER SECTIONAL DENSITY THAN THE LIGHT ONE. In a recent test, a 500-grain hard-cast .457 bullet travelling 1550 FPS MV out-penetrated solids of the same caliber and similar weight that were fired at 600 to 700 FPS FASTER. "and following directly from this can we substitute velocity in lieu of mass in the penetration equation?" As a negative factor - ie, the added velocity reduces penetration. But by how much? This is bound to vary, but is not a linear relationship, and other factors, such as bullet construction, shape, and stability also apply! "Bitte, trinks du nicht das Wasser. Dahin haben die Kuhen gesheissen." | |||
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So, let's do consider the "Solids". I believe what some of you are saying is if we take a bullet of the same caliber, same weight(and therefore SD) that the "Profile" will have no effect on Penetration. I don't believe I can agree with that. Let's say we have two "Totally Solid" bullets(no Lead core and no hollow point) of 30cal weighing 180gr and we pushed them at the same reasonable Velocity from a firearm. However, one is Spire Pointed and one is Cylinder shape. Only difference is the Profile. I believe some of you think they will both penetrate the same amount, and I just don't agree. | |||
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This cannot be a valid discussion without including BULLET SHAPE as one of the factors. | |||
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Well, one can play with velocity changes and change the formula a little, but still, the bullet with the greatest SD has the potential for more penetration. But lets say that I go to the store and buy the same brand of ammo, same caliber, with similarly constructed bullets, except that one bullet has a greater SD than the other. In this case, one may be faster that the other, both both are loaded to their individual velocity (one may be faster). Even so, the one with the greater SD has the potential for greater penetration when fired from the same rifle, and into the same medium. There is lots of data to back SD all over the Internet, reloading manuals, etc: http://www.chuckhawks.com/sd.htm | |||
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I'll accept all that Alf.  The others here don't seem to want to understand your question, especially the one making the quip about bullet shape. Assume best nose shape (truncated cone flat nose  ), then it is not a factor, then get on with mass, velocity and caliber.Then come back to nose shapes, bullet materials, driving bands, and etc. for expanding bullets when you want to get complicated, and then you must specify the medium being penetrated. Lay the foundation before you put the roof on! | |||
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First of all, thanks, guys! This is interesting. Hypothesis: Energy of a bullet is expended in crushing tissue, and breaking its internal connections. If you assume simple isotropic tissue, and a simple, cylindrical bullet, then it seems possible to say that two such bullets, with equal impact energy, will convert their energy to equal volumes of destroyed tissue. A short, fat bullet will sweep out the same volume as a long skinny one, and the long skinny one will leave a longer wound channel. True or false? Or even close enough to being true to be useful?? Prove all things; hold fast to that which is good. | |||
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Really nice Alf! If only they were legal for all African DG, the rifles in .338 Lapua chambering would take over. I too enjoy shooting a couple of .338 Lapuas, a couple of .458/.338 Lapua Magnums, and the piece de resistance, the .375 Lapua, or 9.5x69mm Tornado, is on the build.  | |||
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denton, Your question seems simple at first, but the complexities of the medium and bullets involved make it more involved than a straight forward true or false. I think you will have to get into Alf's higher math and figure out the constants to apply to approximate the particular situation to be able to answer that one.  Or just shoot it and measure it. Kill it and grill it. | |||
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BTW Alf, Is that a Sako or Dakota Longbow? All those funny rifles look the same to me.  Looks like Optilocs holding the scope, so I reckon it is a Sako. | |||
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Alf, On the surface that 338 Lapua does not fit your profile 450 No 2 with all those double rifles suprised me when he came out with he owned Weatherbys and Blasers. I nearly passed out. Mike | |||
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Come on, ALF. Besides a good bullet (right construction and plenty of SD), it's just plain old speed, and every wanker with an HV cartridge, a long barrel, chronograph and several five gallon buckets ought to know that. Mike Wilderness is my cathedral, and hunting is my prayer. | |||
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Dutch pointed out the other day that a deer rifle will separate a cat from three of its four feet. Are you calling that overkill?  Sorry, couldn't resist. Prove all things; hold fast to that which is good. | |||
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Penetration : what factors are most important? I always thought lubricant was the most important. for every hour in front of the computer you should have 3 hours outside | |||
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I want good penetration, I don't follow all of these boring statistics, instead I load a good old round nose, with high sectional density if available in the caliber I am carrying. If not, then I use a ballistic tip at under 2700 fps MV or use a partition, period. Match the bullet for the game, know what sane limits are on distances to shoot, and place your bullet in the right spot. Beyond that, it is strictly academic isn't it?? Cheers seafire | |||
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Hey RIP, Apparently you are correct in that I misunderstood the original question. When I read frontal area I did not realize you all are only talking about Truncated Cone, Round Nose or Cylinder shaped bullets. Apparently that is because I see no reference to it, or overlooked it. But, it doesn't matter, cause the same age old methods of determining what penetrates the best still works. | |||
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Agreed! When we get down to what is practical in a hunting rifle, we are right back to the traditional calibers, bullet and rifle weights, and velocities that have stood the test of time ... or not very far from them. The reason we can deviate at all is the great new bullets that are trying to rewrite the rules. That is what we are quibbling about here. Oh yeah, scopes helped too. If we all used iron sights and old-style bullets, we would still be stuck in the rut of perfection. | |||
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Amen Alf! My middle boy was distinctly unimpressed with the 5.56 in Iraq in 2003. He did his best to scrounge up an M-14 in 7.62. Failing that he traded duty positions with another soldier and ended up using a 50 caliber BMG while mounted and a shotgun during room clearing. He said the 50 BMG pretty much trumped all other arguments. lawndart  | |||
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Rifling twists! If we speak of long bullets against short, heavy against light, fast bullets against slower, nose shape, penetration mediums, penetration depth, calibers, long monos and bearing surfaces, and on and on... Perhaps in the foundation RIP refers to above we might mention rifling twist. Faster twists than the long time standards. Not only for the exploration of L - O - N - G high SD bullets, but also the effects of standard bullet weights being overdriven!! Some of us are seeing penetration enhanced... particularly straight line and head on penetration! by "overly" fast twists! We certainly don't need another "variable" in our solid's now "unchanging variable" by our wonderful nose shape turning sideways on us!..... BigRx | |||
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BigRx, Right on! Faster twist and tougher bullets. You cannot overstabilize a bullet at hunting ranges. Maybe past 1000 yards it makes a difference, but certainly the more the merrier within 500 yards, and the closer the better too for "going to sleep." 10" twist is wonderfully accurate in .404 Jeffery. A tough bullet like a North Fork can handle any rotational stresses. The more the merrier for penetrating solids and expanding softs: TWIST!!! Yep, that is another one of those details. | |||
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Hey RIP, By golly we are in complete agreement. We sure are living in the very best of times for "Bullets". Amazing to see just how great some of the bullets currently available perform On-Game and Accuracy wise too. I can think of quite a few Deer, Hogs and Bear that simply could not have been shot without a scope. I do love to hunt with Iron Sights because I grew up using them. But a scope just allows "Clean Clear Shots" during the twilight period at both ends of the day that "I" could not take otherwise. And scopes have saved some Button Bucks that appeared to be healthy Doe. Got the scope on them and there were the small spikes of a first year Deer. Give them good nutrition and the ones born in April can have small 2"-3" Spikes their first year. Anyway, yes indeed we do have some fine bullets. And I completely agree they skew the old penetration Standards a bit - in a good way if what you hunt needs a lot of penetration. | |||
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Although constraind to handgun ammunition, I have at http://stevespages.com/page8f.htm what I termed "terminal performance". The charts show data of many factory loads, and hand loads, using many different bullets and several different firearms. Some have complained that water is not suitable as a medium for evaluation purposes, however, it is excellent for consistancy. There are drawings of the penetration of bullets in water jugs, and photographs of bullets recovered. About the only constant is the inconsistancy of the results. Take a look... | |||
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