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Ah, I missed the "Larger" part. I wouldn't expect you to have any penetrations issues with the 200gr Hotcore. If your Fed is a semi-auto, I also suspect they feed and function well. | |||
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A bullet does travels slightly nose up (caused by the spin off the bullet, creating the air flow to puch the nose upward) through out its flight this affects BC, not SD. SD is a wieght to diameter factor, thus a bullets SD does not change in flight only the BC is affected by the slight nose up travel _____________________________________________________ A 9mm may expand to a larger diameter, but a 45 ain't going to shrink Men occasionally stumble over the truth, but most of them pick themselves up and hurry off as if nothing had happened. - Winston Churchill | |||
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And the drag is the BC. True SD plays a part in the drag, but so does the shape of the bullet. A bullet with a.313 is still .313 even if the bullet is launched backwards, but the SD is stil .313 _____________________________________________________ A 9mm may expand to a larger diameter, but a 45 ain't going to shrink Men occasionally stumble over the truth, but most of them pick themselves up and hurry off as if nothing had happened. - Winston Churchill | |||
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That seems to presume the rotational skin effect on the spinning bullet point is greater on the downward moving side than it is on the upward side. Accomplishing that would require the downward quadrant to spin faster than the upturning quadrant OR there is a Harry Potter effect going on in there somewhere. I'm not a ballastician but I sorta doubt either of those happens. ?? | |||
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http://www.longrangehunting.co...ft-does-exist-25848/
_____________________________________________________ A 9mm may expand to a larger diameter, but a 45 ain't going to shrink Men occasionally stumble over the truth, but most of them pick themselves up and hurry off as if nothing had happened. - Winston Churchill | |||
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  All you Catapult users feel free to join in. | |||
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ALF: Who cares about the SD or BC of a sideways bullet. If my rifle is keyholing, it's time to switch to a shorter bullet. Besides, when choosing a bullet, the ONLY sectional density i'll ever be able to measure is the one when it's setting on the loading bench. I have yet to see a deer with a high speed camera, that could get it perfectly level and turn it on before my bullet hit him. Until I find one who can, I don't think the theory of dynamic SD will really help much in selecting my next rifle bullet. | |||
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I would want him to stop the bleeding before he treated my hang nail. Alf, I actually understand what you are saying, but I can't manage what I can't measure, so it makes the distinction between a static and dynamic SD worthless during the selection process of my next hunting bullet. Let me ask it another way, since thse dynamic SD's are so valuable, what loading manual can I find them in? | |||
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Alf, I think you understand it better than I do but I still find it alarming at how narrow focused our brethren are regarding a subject that is so important. In one breath they are complaining about poor terminal performance but in their second breath they don't care to understand the numbers. It is really not that difficult of a concept to understand. You've used a more technical definition and I tried a simpler explanation but you have heard the old expression, "you can lead a horse to water but you can't make him drink". Captain Finlander | |||
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SD w/o taking bullet construction into account means very little. SO final SD, after the bullet has stopped, should be the real consideration. A bullet that blows off half the nose & leaves little base left has had it's SD shrink significantly. A premium or monometal bullet that holds together & expands, still maintains most of it's SD. That seems to work for me in choosing a bullet to hunt with, along w/ a decent BC for ranges beyond 150yds or so. LIFE IS NOT A SPECTATOR'S SPORT! | |||
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I concur with Alf's explanation and could not put it better myself. Alf if I may quote yourself from way back then (24 Dec 2006):- "I just need to clarify something for the speed over mass freaks In 1982 Karl Sellier published in his book Shusswaffen und Shusswerkungen, Second edition: his tests on the effect of increasing velocity in lieu of mass in non deforming stable projectiles specifically with regards to the issue of SD and penetration. They also validated this by means of experimentation and a valid mathematical derivation that would explain at the hand of energy transfer to target what happens when you speed the projectile up by trimming weight as Gerard suggests with his FN bullets. The results of the tests show the following: 1. An increase in SD leads to less energy transfer to target per unit distance penetrated and thus deeper penetration. The lower the SD the shallower the penetration, the bigger the energy dump to target and the bigger the TC." SD is a ratio that embodies bullet weight and diameter, and is thus always inherently there. It is a derivative ... you have to change either the weight or the caliber to get the answer, which is the new SD. SD must not be used in a silly way by making cross caliber comparisons, nor across differently constructed bullets, but to have value you have to stick to one caliber for a comparison. For example, take the 7x57 mm, and you decide to use Barnes-X bullets, and the options available to you are 140 gr, 150 gr and say a 160 gr that are sitting on the shelf. 3 options, and you intstinctively ask the salesman to hand you a box of 160 grainers. You have now discriminated against the 2 lighter bullets, and opted for a higher SD bullet. Instinctively most novice hunters decide on bullet weight for his application. The heavier bullet translates to the principle that you want more weight behind the frontal area (Xsa). As weight is favoured in our ballistic system over velocity, the higher SD bullet (of the same type & construction) will out penetrate the lower SD bullet as in the scenario mentioned here. Also, at lower velocity in-target drag is less. This is the value of higher SD (up to a point that its stability is not compromized), and that is the only way we should look at it .... yes, with 'ifs' and 'buts' if you will. In our ballistic system, a higher SD value comes with more MOMENTUM and less ENERGY. And this is the point that Karl Sellier makes above in Alf's quotation. We don't walk into a shop and ask for a high SD bullet with a specific number, we do it instinctively based on bullet weight, as being the simplest entity or unit of measure. Dynamic SD is when the bullet hits the target and a multitude of things can happen - the angle of attack, a bullet flipping over back to front, a bullet attempting to progress sideways, a bullet that does not open up, a bullet that does open up asymmetrically or losing one or more of its petals, or losing all its petals to form a flat fronted cylindrical disk, etc. With controlled expansion bullets in-target stability comes by way of dart-stabilization where the COG point shifts forward as the bullet expands, and by having even expansion for straight-line penetration. Thus terminal SD is now different from pristine SD, but that is what we want so the larger frontal surface can ounch a bigger hole. With non-deforming Solids, in-target stability comes by way of bullet dimensions and how it acts or behaves in terms of its overturning moment propensity. Terminal SD may be the same as its pritine SD as long as it stays point-on, but when it flips it changes to a dynamic SD condition. Warrior | |||
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Alf, on a technical level, your details are very good. You are correct that it's amazing how many "shooter" think that only 55gr 5.56mm bullets | |||
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Thank you for sharing ALF. What about bullet spin and its effect in preventing tumbling on target? Will choosing at shorter/faster hunting bullet reduce chanses of bullet tumbling in game? Or is it more importatnt that the bullet strikes square head on? Not that I have ever confirmed tumbling to happen with a bullet that held together, but still. And those who havent read the article I linked to earlier in the thread should. To me it put some theory behind experiences. | |||
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Alf, i really like reading your perspective in some of these threads. Being a Engineer, I have to ask, what does Thermodynamics have to do with any of this?? It is simple "dynamics/ physics". I fail to see any involvement in heat transfer into the equation. Very seldom do I enter into these discussions; I grin a lot as it is my perception that most folks just regurgitate what they dig up off the internet with little understanding of what they are posting. I AM NOT labeling you with this stigma. Help me understand your application of Thermo into the equation. Just interested. EZ | |||
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Were they testing this with hand loads in a bench gun, or factory loads in a hunting/infantry rifle? | |||
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One must not fail to conclude that the thermoplastic residue of the reaction of the projectile as a ratio to the directed velocitimeter cannot be realistic when the nodes of the vibration are elastic. It must be observed that whatever the approach angle of the terminal path, the vectors must align with the incidental and proposed trauma channel. There have been many thesis written to conclude that both the ballistic coefficient and the sectional density can be obfuscated to the point of inelasticity and that can cause repercussions in the terminal path at impact. Would you also like to discuss foot-pounds of energy? /////////////////////////////////////////////////////////////////////////// "Socialism is a philosophy of failure, the creed of ignorance, and the gospel of envy, its inherent virtue is the equal sharing of misery." Winston Churchill | |||
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My cranial orb hurts. | |||
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Alf, Very interesting - modelling from one of the scientific community who is at the forefront. I noticed that he is a "Professor at Mälardalen University and a member of the Board of Directors at International Ballistics Society. He was also a past chairman at IBC, Research Director, Scientist at FOI, Swedish Defence Research Agency, Senior Principal Research Scientist at DSTO Australia / Materials Research Laboratory." I am sure it would provide an interesting perspective on the view of what governs in-target stability vis-a-vis twist rates, bullet dimensions, distribution of bullet mass, the overturning moment, the role of a flat Nosed bullet, sharply pointed ogived bullets, etc. Would love to see his formula. Is there a way you can post some of that? Thanks Warrior | |||
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Hot Core, We are looking for contributions here. Is this the best you can do? Warrior | |||
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Another thread gone to pot in a hand basket! But funny as hell I must say! | |||
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Rolltop, I don't think so. Perhaps you can help us to learn more and discover some other thruths as we struggle our way through ... that is what the forum is all about. Please participate buddy. The question of in-target stability is till very much under discussion here at AR with regard to the role of twist rate. To describe how stable a given projectile is, we use the gyroscopic stability formula or factor (Sg). Generally we want a factor of 1.3 or greater for rifle rounds. An Sg of 1.5 to - 2.0 has been generally accepted as a good value for 5.56 rounds military rounds under all conditions, even the coldest.. Since the stability factor formula is based on the density of air as a medium it does not cater for the medium of flesh. A high enough barrel twist can never be made to operate with bullets to fulfill the condition of in-flesh stability. Other factors must take over to provide straight-line penetration in flesh. At some point an overly fast twist barrel will cause bullet stripping and slippage in any event; so its impracticle. Let us take the 5.56 mm M193 military bullet with the following data: axial moment of inertia (A) = 11.82 gm/mm2 transverse moment of inertia (B) = 77.45 gm/mm2 mass (m) = 3.53 grams reference diameter (d) = 5.69 mm Using the gyroscopic stability formula: Sg = A2 p2 / (4 B Ma) and assuming sea level, we use an air density of 1.2250 kg/m^3 and discover that this projectile will need in the order of 236,000 rpm for good stability at a level of Sg > 1.3. At 3,200 fps M193 bullet is typically spun up to more like 256,000 rpm with a 1:9" twist, so that Sg approaches a value of 1.9 or 2.0. A barrel twist of 1:12" will spin bullets at around 192,000 rpm and A barrel twist of 1:14" will spin bullets at around 165,000 rpm. Through human flesh (which varies from 980 - 1,100 kg/m^3 or about 1,000 times the density of air) something in the order of 95,000,000 - 100,000,000 rpm is needed to stabilize a projectile at speed if we want to use the Sg formula as reference point. Given the discrepancy, it is clear that the differences between barrels with 1:9 or 1:12" or 1:14" twist rates are not enough. In other words, the bullet is still going to be upset by a transition from air to flesh and overturning becomes a reality if not countered by other factors. Warrior | |||
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That would be like a dog chasing a car and catching it. I will prove this. The pure google in the post above implies that Warrior has a good command of that which follows after: "Let us take the 5.56 mm M193 military bullet with the following data:" Now, Warrior, tell us: If the reference diameter of 5.69mm changes to 5.74mm, what is the rpm required to maintain a stability factor of 1.3? I have one more question: Warrior and Alf, which part of "So, for the sixth time: When the bullet is fully submerged in the target medium - You are right. Rotational velocity cannot work in this context. Agreed. Yes. No argument on this. Yes. Yes. Yes" do you not understand? | |||
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It's easy to see why you folks don't get along....you simply don't understand each other.... That's OK however....no one else does either!   /////////////////////////////////////////////////////////////////////////// "Socialism is a philosophy of failure, the creed of ignorance, and the gospel of envy, its inherent virtue is the equal sharing of misery." Winston Churchill | |||
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The bottom line of all the rhetoric is that the longer/leaner projectiles perform better inside game than shorter/fatter ones of the same caliber. Captain Finlander | |||
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Actually, I understand alf and warrior's "actual comprehension" of the subject. That is why their responses are so - | |||
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Actually, it depends on how they are Designed to function once they make Impact.  | |||
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Captain, If you make short or criptic statements like this, you leave yourself wide open to attacks on this forum if you do not mention a whole list of conditions to qualify, but I do understand what you mean and I can put it in context. Sectional density is alive, although hidden. But we also have to recognise that it is tempered by the bullets geometric dimensions, mass distribuition around its COG and its nose profile as to how it will work in a dynamic way once it engages the target with a given agle of attack, which Alf has mentioned above. The the angle of attack, at time of the bullet impacting the target, depends on 3 stability criteria, namely,the static stability, dynamic stability and the tracking criterium. (See definitions ... http://www.fulton-armory.com/fly/stab.htm) All have to be satisfied to make the projectile 100% aerodynamically stable. Since all three criteria cannot be satisfied 100%, the projectile will always sit at some angle of attack even though we tried to stabilize the bullet by adequate spin by virtue of the rifle's barrel which is mostly a given that we have to live with. Gyroscopic stability as calculated by Sg (also referred to as SF = Stability Factor) at the muzzle gets bigger downrange and so improve the one criterium. But the angle of attack also gets bigger downrange over distance and so working seemingly in opposion. Thus a bullet can have a large angle of attack, but still be gyroscopically stable in terms of its Sg value. At practical hunting ranges between 80 to 300 yds it is not a common problem that we encounter every day, unless something (barrel or bullet) is way out of kilter or out of the norm. However, a large angle of attack does not imply instability, it simply implies that the long axis of the bullet is sitting at an angle to the direction of it's trajectory or its direction of forward motion. In terms of in-target stability of the bullet, it now comes down to the bullet's geometry and construction and not on calculated higher SF values taken at the muzzle (Sg increases over distance in any event). The bullet's geometry essentially captures its axial and transverse moments of inertia. In-target the bullet adopts a Dynamic SD (as mentioned by Alf) in terms of its forward motion by its wetted surface and ultimately by flipping over and coming to a stop due to the forces of drag or may be even straight-line penetration right through. The reason why Solid RN bullets or Ogived FMJ bullets or Spitzer Mono Metal Solids overturn in target is due to the fact that its COG point lies aft its geometrical mid-point and so induces an overturning moment when it meets the in-target drag force (to the square of velocity) and the bullet has an inherent or by its very design an inability to control the angle of attack - as the bullet is not shaped as a round ball. Once the bullet has flipped over, the COG shift forward and it becomes dart-stabilized. The reason why FN Solids penetrate straighter than a RN Solid is due to its better mass distribution around its COG point and its flat meplat that assists to better damp out small angle of attacks. With regard to Softs or more particularly CEB's that mushroom asymetrically without losing some of its petals, the bullet's COG point shifts forward, as the bullet mushrooms to form a shorter bullet being front heavy and so it remains stable in-target by penetrating as straight as can be, unless deflected by encountering a major bone at an oblige angle that could change its direction of motion. In the unfortunate event that an ogived solid bullet gets its nose plugged by bone, it will overturn due to drag by virtue of its new geometrical condition that prevents expansion, and thus its propensity to overturn. This might not be ideal for straight-line penetration, but when it flips through the heart and lungs it will cause massive wounding (ie bleeding) and be very effective in the killing event, and this is what luckily happened with RIP's first buffalo. The problem with a tumbling bullet is when it misses the vitals or get stuck in the grass filled rumen. Again, Dynamic SD is at work. Warrior | |||
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Some real gems here:
 Says he who cannot muster the brain cells to reply to this: "I will prove this. The pure google in the post above implies that Warrior has a good command of that which follows after: "Let us take the 5.56 mm M193 military bullet with the following data:" Now, Warrior, tell us: If the reference diameter of 5.69mm changes to 5.74mm, what is the rpm required to maintain a stability factor of 1.3?" At what distance does this tracking criterium become important?
This is too funny when you pretend to know this stuff. Where do you get this from? Thanks for the mirth and entertainment though, we will have a good laugh when I show this to some friends. | |||
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My cranial orb is now throbbing.  | |||
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