gerard
May 22, 2017

Energy, momentum, sd and cross sectional area.

32 comments

There are many different aspects about this subject and each has the hunters that will swear by their method. What are your thoughts about this?

bullet.behaviour
May 22, 2017Edited: May 26, 2017

Welcome Gerard,

 

Amper begin ek in Afrikaans...

 

You may wish to read my articles on THE MYTHS HERE.

 

Briefly my off the cuff position is the following:

  • Kinetic Energy is a scalar entity which can not do work. It has only one effect and that is on the carrier of the KE, namely the bullet. As the kineses diminishes during its flight and particularly after impact kinetic energy is translated as heat energy into the carrier of the KE. It has no killing ability.

  • Momentum has only value when the retained momentum of the bullet is considered after impact: Loss of mass / loss of velocity due to profile drag need to be allowed for.

  • Sectional Density is a theoretical figure related to static pieces of pretty bullets while they reside in their box. Impact destroys that figure to a useless value. The published figure has no bearing on penetration ability unless the bullet is a solid mono-metal design with no frontal expansion. OR, if:

  • there is an accurately predictable and consistently repeatable expansion to a new known frontal cross section, then

  • integrating the retained momentum with the expanded frontal cross section (modified sectional density) produces an impulse value. When compared to a known norm this impulse value can be used as a relative penetration index (RPI) and a prediction of penetration can be tabulated as I have done HERE.

 

gerard
May 23, 2017

It seems that we are thinking along the same lines. I have said many times, regarding energy for short, that only a comparison is necessary. Take a 180gr Match King bullet from a 30-06 and shoot a kudu sidways on, on the shoulder, at 50m. The bullet will probably blow up on the shoulder, not penetrate to the chest cavity and the kudu will run away, to die later. The bullet has expended all it's energy on the animal. By the same token, take the same shot with a Swift A-Frame and the result will probably be an exit wound, with the bullet expending some energy behind the animal. The result will be vastly different and, if the animal runs, it will only be for a short distance. Both bullets are made from lead with a copper jacket but the difference lies in the design. It depends on what the bullet is designed to do and not the energy it carries with it.

bullet.behaviour
May 24, 2017Edited: May 27, 2017

The effect on the carrier of the KE is not only a function of the design but is at the same time related to the amount of bullet mass (matter) available to absorb the kinetic energy translated as heat into it.

 

The reference example I used in my article in The Myths (also published in SA Hunter magazine) is that of a 180 gr bullet from a 300 RUM impacting a Cape buffalo shoulder from 40 yards compared to a 500gr of similar design from a. 458 Lott. Both have exactly the same kinetic energy values at impact but the effect on the buffalo will rapidly change the facial expression of the RUM shooter.

 

By the way, despite containing identical scalar values of kinetic energy the impact momentum / impulse of the slower by 1,200 ft/sec 500gr bullet is almost 2x that of the high velocity 180gr.

 

The only effect of translated kinetic energy is a scalar increase of the heat into the amount of matter (mass) of the bullet. This weakens the material. If the mass of the bullet in relation to the scalar value of the kinetic energy is too little, including the mass of the jacket design, the jacket fails. Lead at that heat value flows, loses surface tension and separates. Retained mass and retained momentum is all that counts to penetrate and mechanically shear the vital organ and its neuro impulses in its path.

 

Gerard I have a question for you, please: The retained momentum force after expansion onto the new frontal area - or more correctly stated: impulse - is a product of the modified frontal area of the expanded nose section of the bullet after impact and its mass in movement, pushing it along. The question will be about profile drag differences through the meat, bone, tendon and skin fibres the bullet encounters:

 

Assuming both the recovered bullets shown underneath from a .375 H&H had a 1.5x calibre expansion and had exactly the same original weight - and weight retention, impact velocity and shot placement. Will the broken up (smaller) frontal area of the open petals design have a lower frontal drag value as opposed to the solid perfect mushroom of the other?

 

 

My present thinking is that even though the larger frontal area of a solid mushroom should create more frontal drag than open petals, the rougher cutting edges of the latter will cause much the same profile drag in practice.

 

This Peregrine 300gr VRG-3 bullet from the Peregrine website is said to have penetrated both shoulders of a Cape buffalo bull and was stopped by the opposite skin. Expansion appears to be the ideal 1.5x calibre.

 

 

Below is a photo enlarged from the GS Custom website. Expansion appears to also be 1.5x calibre. The smaller frontal area than the perfect mushroom is obvious - and so is the pronounced cutting edges of the petals.

 

 

This 340 gr Rhino Solid Shank Bullet from a .375 H&H into a giraffe shoulder from about 60 yards penetrated all the way through and stopped against the skin on the opposite shoulder. It expanded to exactly 2x calibre size and retained 99% of its original weight. When I removed it from the scapula I was amazed that despite this large frontal area it still had penetrated through all that distance of giraffe hardware.

 

Hunters who for the first time observe the almost 1" thick skins of buffalo and giraffe immediately realise the folly of even considering any cup and core bullet for these animals.

frhunter13
Jun 9, 2017

I got my first experience with the bigger, slower concept many years ago using a smoke pole. At that time my go to rifle was a Remington gas operated 3006 semi auto shooting 150g Remington or Federal soft points. These did the job fine but many times recovered in the off side hide. So come smoke pole season I shot a buck broadside with my brand new Hawkin and a 480g Maxiball going a meager 1350 fps. Blew that deer right off its feet with a clean 50 caliber hole through both shoulders. That was my first hint that Bigger, Slower = Better?

gerard
Jun 9, 2017

You mean grains not grams but, that is besides the point. Would you attempt the same shot at 200 yds? With a 30-06 with a 150gr bullet, a 200 yd shot is do-able. That is the downside of slow and heavy.

frhunter13
Jun 9, 2017

Not at 250 yards, no sir. For that I have a 3006 and 180g(rain) interlock at 2880 fps but it has slowed down quite a bit at 250 yards. I do not use this rifle if I know the game will be inside of 150 yards.

 

All around I prefer the 35 Whelen or 358 Winchester with 225 or 250g hard bullets at 2400 to 2700 because I get the average of game drops dead and less meat damage. The 358 Winchester sees plenty of action with 225g bullets at 2400 fps. If I am using Factory ammo in my single shot Whelen it's Remington 200g Interlocks at 2685 fps.

 

However, in the constricted woods were I do most of my hunting, it is now with a 45/70 double with hard bullets.

 

To note. Recently an American hunter took the big five with a 45/70 lever rifle and some really hard lead alloy cylindrical bullets. The Cape Buffalo was shot at 200 yards, and then again at 100 yards. This was by a fellow who proved 1600 fps gives more penetration than 2200 fps., at least in the mediums he was testing. This has to do with the non compressibility of fluids. Take your hand and slap the water real hard, then again sedately. There is a difference you can feel. Simplistic yes, but his big five hunt was to prove that point.

gerard
Jun 11, 2017

https://en.wikipedia.org/wiki/Gram

https://en.wikipedia.org/wiki/Grain_(unit)

 

The abbreviation for grams is g and the abbreviation for grains is gr.

 

Something that many people do not take into account is that subsonic is the way we think and supersonic is somewhat different.

 

Generally, when an expanding bullet is fired from a hunting rifle, the penetration will follow a bell curve. At short range, where speed is high, penetration will be a certain depth. As range increases and speed drops, penetration will increase. As speed, due to distance, drops further, penetration will decrease again. All this is governed by the shape of the deformed bullet and the retained momentum that the bullet has.

 

Generally, when a solid bullet, that deforms little when meeting a target, is fired, penetration increases with speed, until lack of momentum causes it to decrease again.

 

The above two scenarios are tempered by the media the bullet meets and the shape that is presented to the direction of travel.

 

The surface area presented to the direction of travel slows the bullet down and the shape of the front of the bullet is instrumental in how much damage is done. For example: A double caliber round mushroom shape will do less damage than a flat shape at the same speed.

 

 

Andries
Jun 11, 2017Edited: Jun 11, 2017

Gerard - almost as if you were anticipating my planned posts in the new category I opened...

 

Bullet designs have been following the Bernoulli theorem for in-compressible fluid flow and do so to this day. What is more, very little knowledge exists outside the few real researchers. Like man-made global warming theory it is hard to pass by the established dogma of the gun religion.

 

It is so strange that the facts of supersonic aerodynamics have never been adopted by any of the traditional bullet manufacturers. The first proper design for minimum drag airflow I saw was on a 300gr RWS I used in m .375 H&H in old Rhodesia - straight shank and sharp cornered into a straight conical nose. And then the knowledge of the effect of the very dense in-animal environment on the bullet is very limited as well.

 

Resistance to change is a terribly limiting mind set - easier to shoot the messenger. The media is adept at this.

frhunter13
Jun 11, 2017

Actually Hornady has addressed supersonic with a new material on their ballistic tip. I don't think thinking will change easily that a flat tip has better BC. The instruments belie that point. As soon as I see published BC values (and believe me the military has them to a nat's ass), these I believe. Not theory.

 

FYI take a look at this:

 

http://the4570inafrica.blogspot.com/

Andries
Jun 11, 2017Edited: Jun 11, 2017

I do not think there is any dispute that a pointed tip bullet has better aerodynamics than flat tips. The best supersonic aerodynamic nose shape in fact is a true cone with sharp corners to the parallel surface of the shank. In the final instance the hunter wants the bullet which performs best inside the animal and if that means giving up on some aerodynamic elegance that is O.K.

In practice even the aerodynamics have a very small influence. I see no practical difference in impact point at 150 yards between the Peregrine 168gr semi flat point VRG-3 bullets from my .303 and the spitzer PMP 174gr. Penetration of the Peregrines through wildebeest shoulder is better due to better terminal dynamics.

gerard
Jun 11, 2017

You are right Andries. I was referring to cylinder shapes vs. round mushrooms, of the same diameter, in terminal ballistics not external ballistics.

 

The three main 'ballistics' that everyone talks about are internal, external and terminal ballistics. There are two areas that are little known in between each of those three called intermediate ballistics (in the cloud ahead of the muzzle) and transitional ballistics (when the bullet transitions from flight to entering the target).

 

BTW. I read the entire article linked above and it ends with: "The 45-70 is a quintessential American cartridge, big medicine for moose, bison, elk and brown bear. But the African hunter may well come across some crusty old dugga boy who has never heard the tales told around a Western campfire, is no cousin to the mean-spirited but thin-skinned grizzly, and who will take one contemptuous look at that lever-operated stick and utter the chilling Cape buffalo equivalent of “Go ahead, make my day.” "

 

I will go with that :-)

Andries
Jun 11, 2017

Go ahead, make my day...

As I have said many times before - buffalo hunting is mostly a walk in the park - sometimes a long walk as forum member Rick can testify to. The moment the bullet diameter (read 'frontal area') goes wider than .375" the profile drag rise through sinew, muscle and bone is such that the effort to impart the necessary impulse (momentum onto frontal area) AND stay nose ahead becomes a challenge. Propellant volume is required - the reason why I have fallen in love with the .416 Rigby.

 

All this is the bottom line why Michael is working towards minimum 2,350 ft/sec with the 458450FN bullet.

frhunter13
Jun 11, 2017

Yea. I like that last paragraph, pretty funny. I would never try the beefier of the big five with a 45/70 myself! I did finally reach 2353 with the 450GSC Flat I am hand inserting into the 458 Winny. Not sure about the crimped MAX in the mag yet. Somewhere between 2338 and 2348.

 

As for the cloud of hot gas in front of the muzzle, shoot enough smoke poles and you get a good feeling for that :) One thing I learned with those, put more than 90 grains of loose powder in a Hawkin, it burns the 90 grains and just spits the rest out and messes with your accuracy. To put more than 90 you need 30 to 50 grain pellets and a really hot primer.

Andries
Jun 12, 2017Edited: Jun 12, 2017

I assume Gerard referred to the “gas cloud” at the moment of muzzle exit in the sense of the big influence the escaping gas over the bullet has on the repeated accuracy of bullets. It is both a function of bullet design and of perfect concentricity and edge condition of the crown. It is an interesting exceedingly momentary moment in the short life of a fired bullet.

 

Inside the bore the terms subsonic or supersonic do not apply because these refer to the physics of a body moving in free air causing airflow over its surfaces. So, as the bullet’s nose moves out of the muzzle (at say Mach 2 in the case of the .458 Win Mag) the free air suddenly creates a cone of highly compressed air around it, extending rearwards at an acute angle.

 

Immediate Aerodynamics - Bullet Front End

Two extreme cases exist: The apex of this angle is either attached to the bullet at a sharp point at the nose if the bullet nose is sharp and conical as in the Impala bullets, or the cone angle stretches backwards from a bulbous half-moon shock boundary ahead of the bullet nose and unattached to it if it is a typical old style .458 round nose 500gr bullet. This unattached shock is the cause of immediate and massive drag pressure on the bullet. Air faster than Mach 1 does not like any shape with curved surfaces in its way

 

Similarly, anywhere there is a measurable radius (ogive) to the bullet front end such detached shock waves form with significant increase in aerodynamic drag. Any nose shape where there are sharp corners with insignificant radii changing into a flat surface conical shape makes for less drag in the supersonic airflow.

 

Immediate Aerodynamics - Bullet Rear End

More to the point in this discussion on muzzle departure: the design of the bullet base is of more importance to the shooter than the nose shape regarding bullet stability and eventual accuracy. The high speed-high density gas column from the muzzle overtaking the bullet is the significant constant which influences the many variables in bullet base design and manufacture.

 

Flat base bullets: The moment a flat based bullet slips the muzzle at Mach 2 it gets engulfed and overtaken from behind by the bore-length column of gas containing a density relative to typically 7,000 psi (same as the pressure in an ocean 15 million feet down) and exerts considerable force onto the bullet from behind. This momentary force is much, much higher than the Mach 2 free air aerodynamic moments on the bullet from the front.

Apart from the mechanical displacement on the bullet tail by less than a 100% perfect 90o crown face or other minute nicks in the crown mechanically influencing the concentric departure, the smallest inconsistency in the bullet base allows the force of the outblow to put a lateral displacement into the bullet tail. Gyroscopic precession causes this displacement to be self-perpetuating. Fortunately, machined flat base bullets are invariably of perfect geometry.

 

Boat tail bullets: A boat tail bullet gets rammed from behind by this force even while the rear end is still inside the bore, exacerbating any crown interference. Furthermore the angled surface of the boat tail presenting a positive angle of attack to the ramming gasflow from behind sets the scene for an appreciable lateral displacement of the tail end should there be the slightest inconsistency in the radial concentricity of the changeover from bore contact surface into the boat tail cone, and further on behind this radial.

 

Reverse Airflow

As the compressed barrel gas bursts onto the bullet from behind the following happens momentarily:

  • The free stream air over the bullet is reversed and the dynamics are as if it is flying backwards into very dense water.

  • Very strong conical shock waves form on the bullet, coned forward.

Then as the hot gas pressure disperses into a cloud around the bullet there is another moment of zero air flow where the bullet with forward centre of mass receives no aerodynamic stability input, whereafter the normal Mach 2 stability interactions of aerodynamic and inertial moments resume and the bullet starts slowing down due to aerodynamic drag. This slow down lowers the kineses which progressively lowers the scalar joule value of kinetic energy contained in the bullet, translating its potential heat into real joules of heat energy in the bullet.

 

From here on the design of form and its interactions with the dynamics of supersonic flight drive the study of its ballistics.

 

When considering the principle of form follows function it is evident that bullet design in the US has for many many years followed the premise that flight through air was its main function. A “flat shooting” form has been the driver, and not the performance into and through the very dense substances of skin, sinew, flesh and bone. The designs of the Barnes and the four makes of premium bullets from South Africa presented in the category Big Beasts, Best Bullets have one function in mind: in-animal-performance.

frhunter13
Jun 12, 2017

Added to this complexity is the motion of the muzzle as the bullet exits. The tube oscillates, the thicker the tube the higher the frequency a lower the magnitude of motion. As the barrel heats up, if the steel has any cold stresses, they will be relieved progressively by the heat and the shots will walk. I have seen the high speed videos. The bullet wobbles and then stabilizes. The more the wobble the more energy is lost and the more accuracy is affected. The super long boat tail bullets stabilize faster. The bullet path has a lateral component of motion created by muzzle motion. The trick is to have the SAME muzzle motion with each shot regardless of how hot the barrel gets.

 

An example of this is my Ruger 3006 which walked it's shots. I had the receiver trued and the entire metal assembly cryo-treated. This involves and extreme heating and extreme cold cycle. This removed the stressed in the barrel and assembly. Now this rifle is 1/2 MOA and the shots do not walk. Re-fitting the stock and the scope required some adjustments though, because of slight dimensional changes.

 

As for terminal performance we constantly get the dichotomy of clean pass through verses impact shock and massive damage. If you are counting on a pretty and effective kill you lean toward hard, bone penetrating shoulder or skull shots. If you are satisfied with a slower kill or a neck shot, then you lean toward the softer expanding type bullets. That argument continues here in the US certainly, and leans toward the softer. With the heavy boned, dangerous African game you can choose the hard go through the shoulder, or skull, or the wait for a better, softer path to the heart from forward or slightly behind. The shoulder/skull option needs a stable bullet through thick bone. I guess that sums up the requirement.

Andries
Jun 12, 2017Edited: Jun 12, 2017

Barrels of South African built rifles and those made by the local barrel manufacturer Truvello, as well as rifles from Europe, including barrels from Austria and Finland are already stress relieved. No lapping, no breaking in, no bedding required.

 

Many theories have been proposed regarding barrel movement during bullet transit and the resonance of the barrel after the bullet has left the barrel. (Despite what is often read in gun writing, barrel resonance has zero influence on the bullet as it is a reactive, vibratory whipping after the bullet had left the muzzle).There certainly is no symmetric pattern in even the most accurate barrels.

 

Somchem has high speed video with laser measured results of many rifles tested for accuracy. Here is the measured muzzle displacement of a locally manufactured barrel at the moment of bullet exit:

 

Shot 1. Muzzle displaced 6.5 micron right, 1 micron down.

Shot 2. Muzzle displaced 5.8 micron right, 1 micron down.

Shot 3. Muzzle displaced 9.0 micron right, 1 micron down.

Shot 4. Muzzle displaced 8.0 micron right, 1 micron down.

Shot 5. Muzzle displaced 5.7 micron right, 1 micron down.

 

10 micron equals one 100th of a millimetre, which is less than one half of a thousandth of an inch. When considering that 1 MOA represents 1/64th of an inch at the muzzle, the maximum displacement of the tested rifle muzzle of 1/700th of an inch indicates what can be termed as an accurate piece.

 

Maybe this explains the results of the SA Hunting Rifle Group Shooting Competitions with commercial hunting rifles using PMP commercial ammunition as seen HERE.

frhunter13
Jun 12, 2017

Displacement of muzzle less important than tangential VELOCITY of muzzle. I can guarantee this CAN be a LARGE factor in bullet placement because I have seen it myself. Perhaps not with a target rifle or a really high end accurized rifle because those are painstakingly built to minimize it. The actual wave form of the pressure in the barrel made by different powder and / or different bullet cause a different landing point. This is most noticeable with heavy bullets and thin barrels. You cannot avoid the harmonic vibration because it is a physical LAW of string mathematics. As far as stress relief of the steel, it must be at a molecular level. I am really impressed that all the rifles in South Africa are cryo treated! Can I buy one there and bring it home?

 

Many times I have sighted in a rifle with one bullet, only to switch manufactures with a slightly different bullet and it now hits several inches to the right or left. The 35 Whelen for example. 225g Sierra boat tails 1/2 MOA centered 1" high at 100 yards. Switch powder and bullets to 225g Barnes and they land consistently 4 inches right at 100 yards. It's a different wave on the barrel.

 

Plus I am beginning to see a pattern of SA pride here. That's fine too :)

Andries
Jun 12, 2017Edited: Jun 12, 2017

You certainly can buy a Musgrave here but it can only be sent to your FFL dealer. There is a delay while the SA Police clears the export permit. Look at the page of the Musgraves. The factory is 3 hrs drive from me.

 

Here: https://www.bullet-behavior.com/the-new-musgraves

 

 

frhunter13
Jun 12, 2017

Was at the range a few weeks back and met a very large fellow there and we got to talking before the range opened. He had been on Safari for large game, no dangerous and was telling me how much fun he had in Africa. He had used his 338 Mag. His new rifle sported a new German first planar focus scope. He had built the 308 rifle himself using an ordered custom house Remington 700 short action receiver. He had bought the barrel system equipment because he is a machinist. The barrel was very high end USA made. The receiver was cut with a spiral bolt that ran in a spiral track. I saw him push it home with only his thumb and index finger. He bore sighted it and proceeded to move out to 100 yards. Before he finished I saw him put three bullets in he same hole at 100 yards, dead center on his target. I don't think he used 12 rounds.

Andries
Jun 12, 2017

Wow.. That also means he can shoot! That is 80% of an accurate rifle. Pity the rifle will not qualify for the Hunting Rifle Group Shooting Competitions - being custom made - but he should enter surely.

New Posts
  • Andries
    Aug 21, 2018

    Client Michael shot his very old, very large Cape buffalo from 55 yards with the .458 Lott. The 480 gr Peregrine VRG-2 mono-copper bullet went in one shoulder, broke through a rib, took the main arteries off the heart top and exploded the top and bottom chambers on one side, broke though an opposite rib and just missed the opposite humerus, made a calibre size hole through the skin and was gone. The old bull went down in his tracks like a bag of potatoes as if he was brain shot - the first time I have witnessed a heart shot Cape buffalo do that. Impeccable shot placement and outstanding behaviour by the Peregrine flat nose solid. Photos will follow.
  • dcrimy
    Feb 15, 2018

    The bullet on the left is what is left of a Nosler 6.5 125gr Partition. It weights 83grs after almost passing thru a mature muley buck & has expanded to about 33cal. . It struck no bone & was recovered under the hide on the opposite side. The deer went down so you would have to say the bullet worked. The buck was about 80yds away & the bullet was launched from a 260 Rem @ 2950 FPS. The bullet to the right is a Barnes 120gr TSX recovered from the dirt back stop behind my 100yd. target. It was fired from a 6.5-06 at 3235FPS. It expanded to 50cal & still weights 120gr. Years ago I relied a lot on the partition but due to what I see as a superior design I now only use the homogeneous copper bullets like the Barnes TSX & TTSX on elk. I have used the Barnes for years now on heavy game like elk with complete success & have yet to recover a bullet , so I can't display a recovered one. Like wise when the Barnes 6.5 TTSX100gr is used on mature deer it dependably passes completely thru. They perform like a bullet considerably heavier because they tend to retain 100% of their weight. For me this is confidence. Another point is that if a meaty part is inadvertently struck a C&C bullet like the Nosler & others can destroy large amounts of edible meat. The homogeneous copper bullets tend to keep meat destruction to a minim if struck. Since my main reason for hunting is the food source I very muck appreciate the copper bullets.
  • dcrimy
    Dec 12, 2017

    Here is a picture of a Barnes 6.5 120gr TSX I recovered from the dirt bank behind my 100yd target. It is about 1/2" across & still weighs 120 gr on my scale. It was launched from my 6.5-06 at 3235fps which means it struck the dirt bank at about 2970fps. This is a very desirable mushroom shape with the 4 petals being very evident. None broke off. Perhaps bullets striking game will not be as perfect a mushroom . Striking dirt is brutal to a bullet..

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