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# External Ballistics Summary

Submitted by admin on May 3, 2009 - 1:47am
## Forces acting on the projectileWhen in flight, the main forces acting on the projectile are gravity, drag and if present wind. Gravity imparts a downward acceleration on the projectile, causing it to drop from the line of sight. Drag or the air resistance decelerates the projectile with a force proportional to the square of the velocity (or cube, or even higher powers of For medium to longer ranges and flight times, besides gravity, air resistance and wind, several meso variables described in the external factors paragraph have to be taken into account. For long to very long ranges and flight times, minor effects and forces such as the ones described in the long range factors paragraph become important and have to be taken into account. The practical effects of these variables are generally irrelevant for most firearms users, since normal group scatter at short and medium ranges prevails over the influence these effects exert on firearms projectiles trajectories. At extremely long ranges, artillery must fire projectiles along trajectories that are not even approximately straight; they are closer to parabolic, although air resistance affects this. In the case of ballistic missiles, the altitudes involved have a significant effect as well, with part of the flight taking place in a near-vacuum. ## Stabilizing non-spherical projectiles during flightTwo methods can be employed to stabilize non-spherical (ball shaped) projectiles during flight: - Projectiles like arrows or sabots like the M829 Armor-Piercing, Fin-Stabilized, Discarding Sabot (APFSDS) achieve stability by forcing their center of pressure (CP) behind their center of gravity (CG) with tail surfaces. The CP behind the CG condition yields stable projectile flight, meaning the projectile will not overturn during flight through the atmosphere due to aerodynamic forces.
- Projectiles like small arms bullets and artillery shells must deal with their CP being in front of their CG, which destabilizes these projectiles during flight. To stabilize such projectiles the projectile is spun around its longitudinal (leading to trailing) axis. The spinning mass makes the bullets length axis resistant to the destabilizing overturning torque of the CP being in front of the CG.
## Small arms external ballistics## Bullet dropThe effect of gravity on a projectile in flight is often referred to as bullet drop. It is important to understand the effect of gravity when zeroing the sighting components of a gun. To plan for bullet drop and compensate properly, one must understand parabolic shaped trajectories. Due to the parabolic shape of the projectile path, the line of sight or horizontal sighting plane will cross the projectiles trajectory at two points called the near zero and far zero incase the projectile starts its trajectory (slightly) inclined upward in relation to the sighting device horizontal plane, causing part of the bullet path to appear to rise above the horizontal sighting plane. The distance at which the firearm is zeroed, and the vertical distance between the sighting device axis and barrel bore axis, determine the apparent severity of the "rise" in both the X and Y axes (how far above the horizontal sighting plane the rise goes, and over what distance it lasts). Many firearms ballistics tables and graphs show a rise in trajectory at distances shorter than the one (far zero) used for sight-in. This apparent "rise" of the projectile in the first part of its trajectory is relative only to the sighting plane, and is not actually a rise. The laws of physics dictate that the projectile will begin to be pulled down by gravity as soon as it leaves the support of the barrel bore at the muzzle, and can never rise above the axis of the bore. The apparent "rise" is caused by the separation of the plane of the sighting device axis and that of the bore axis and the fact that the projectile rarely leaves the bore perfectly horizontally. If a firearm is zeroed at 100 meters, then the far horizontal sighting plane and the projectile path must "cross" at that distance; the sighting line must be adjusted to intersect with the projectile path at 100 meters. In the case of a bore axis that is maintained in a perfectly horizontal position, the sighting device must be inclined downward to achieve this intersection. The axial separation distance between the line of sight and the bore axis and trajectory of the projectile dictate the amount of angular declination required to achieve the required intersection. ## Drag resistance modelling and measuringMathematical models for calculating the effects of drag or air resistance are quite complex and for the simpler mathematical models not very reliable beyond 500 m (500 yd), so the most reliable method of establishing trajectories is still by empirical measurement. ## Fixed drag curve models generated for standard-shaped projectilesUse of ballistics tables or ballistics software based on the Siacci/Mayevski G1 drag model, introduced in 1881, are the most common method used to work with external ballistics. Bullets are described by a ballistic coefficient, or BC, which combines the air resistance of the bullet shape (the drag coefficient) and its sectional density (a function of mass and bullet diameter). The deceleration due to drag that a projectile with mass Sporting bullets, with a calibre Sectional density is a very important aspect of a bullet, and is the ratio of frontal surface area (half the bullet diameter squared, times pi) to bullet mass. Since, for a given bullet shape, frontal surface increases as the square of the calibre, and mass increases as the cube of the diameter, then sectional density grows linearly with bore diameter. Since BC combines shape and sectional density, a half scale model of the G1 projectile will have a BC of 0.5, and a quarter scale model will have a BC of 0.25. Since different projectile shapes will respond differently to changes in velocity (particularly between supersonic and subsonic velocities), a BC provided by a bullet manufacturer will be an average BC that represents the common range of velocities for that bullet. For rifle bullets, this will probably be a supersonic velocity, for pistol bullets it will be probably be subsonic. For projectiles that travel through the supersonic, transonic and subsonic flight regimes BC is not well approximated by a single constant, but is considered to be a function Most ballistic tables or software takes for granted that one specific drag function correctly describes the drag and hence the flight characteristics of a bullet related to its ballistics coefficient. Those models do not differentiate between wadcutter, flat-based, spitzer, boat-tail, very-low-drag, etc. bullet types. They assume one invariable drag function as indicated by the published BC. These resulting drag curve models are referred to as the Ingalls, G1 (by far the most popular), G2, G5, G6, G7 (used by some manufacturers for very-low-drag bullets), G8, GI and GL drag curves. How different speed regimes affect .338 calibre rifle bullets can be seen in the .338 Lapua Magnum product brochure which states Doppler radar established G1 BC data. ## More advanced drag models## Pejsa modelBesides the traditional Siacci/Mayevski G1 drag model other more advanced drag models exist. The most prominent alternative ballistic model is probably the model presented in 1980 by Dr. Arthur J. Pejsa. Mr. Pejsa claims on his website that his method was consistently capable of predicting (supersonic) rifle bullet trajectories within 2.54 mm (0.1 in) and bullet velocities within 0.3048 m/s (1 ft/s) out to 914.4 m (1000 yd) when compared to dozens of actual measurements. The Pejsa model is an analytic closed-form solution that does not use any tables or fixed drag curves generated for standard-shaped projectiles. The Pejsa method uses the G1-based ballistic coefficient as published, and incorporates this in a Pejsa retardation coefficient function in order to model the retardation behaviour of the specific projectile. Since it effectively uses an analytic function (drag coefficient modelled as a function of the Mach number) in order to match the drag behaviour of the specific bullet the Pesja method does not need to rely on any prefixed assumption. Besides the mathematical retardation coefficient function, Pejsa added an extra slope constant factor that accounts for the more subtle change in retardation rate downrange of different bullet shapes and sizes. It ranges from 0.1 (flat-nose bullets) to 0.9 (very-low-drag bullets). If this deceleration constant factor is unknown a default value of 0.5 will predict the flight behaviour of most modern spitzer-type rifle bullets quite well. With the help of test firing measurements the slope constant for a particular bullet/rifle system/shooter combination can be determined. These test firings should preferably be executed at 60% and for extreme long range ballistic predictions also at 80% to 90% of the supersonic range of the projectiles of interest, staying away from erratic transonic effects. With this the Pejsa model can easily be tuned for the specific drag behaviour of a specific projectile, making significant better ballistic predictions for ranges beyond 500 m (547 yd) possible. Some software developers offer commercial software which is based on the Pejsa drag model enhanced and improved with refinements to account for normally minor effects (Coriolis, gyroscopic drift, etc.) that come in to play at long range. The developers of these enhanced Pejsa models designed these programs for ballistic predictions beyond 1000 m (1094 yd). ## 6 degrees of freedom (6 DOF) modelThere are also advanced professional ballistic models like PRODAS available. These are based on 6 Degrees Of Freedom (6 DOF) calculations. 6 DOF modelling needs such elaborate input, knowledge of the employed projectiles and long calculation time on computers that it is unpractical for non-professional ballisticians and field use where calculations generally have to be done on the fly on PDA's with relatively modest computing power. 6 DOF is generally used by military organizations that study the ballistic behaviour of a limited number of (intended) military issue projectiles. Calculated 6 DOF trends can be incorporated as correction tables in more conventional ballistic software applications. ## Doppler radar-measurementsFor the precise establishment of drag or air resistance effects on projectiles, Doppler radar-measurements are required. Weibel 1000e Doppler radars are used by governments, professional ballisticians, defence forces and a few ammunition manufacturers to obtain real world data of the flight behaviour of projectiles of their interest. Correctly established state of the art Doppler radar measurements can determine the flight behaviour of projectiles as small as airgun pellets in three-dimensional space to within a few millimetres accuracy. The gathered data regarding the projectile deceleration can be derived and expressed in several ways, such as ballistic coefficients (BC) or drag coefficients (C Doppler radar measurement results for a lathe turned monolithic solid .50 BMG very-low-drag bullet (Lost River J40 .510-773 grain monolithic solid bullet / twist rate 1:15 in) look like this:
## General trends in drag or ballistic coefficientIn general, a pointed bullet will have a better drag coefficient (C ## The transonic problemWhen the velocity of a rifle bullet fired at supersonic muzzle velocity approaches the speed of sound it enters the transonic region. In the transonic region, the centre of pressure (CP) of most bullets shifts forward as the bullet decelerates. That CP shift affects the (dynamic) stability of the bullet. If the bullet is not well stabilized, it can not remain pointing forward through the transonic region (the bullets starts to exhibit an unwanted coning motion that, if not dampened out, can eventually end in uncontrollable tumbling along the length axis). However, even if the bullet has sufficient stability (static and dynamic) to be able to fly through the transonic region and stays pointing forward, it is still affected. The erratic and sudden CP shift and (temporary) decrease of dynamic stability can cause significant dispersion (and hence significant accuracy decay), even if the bullet's flight becomes well behaved again when it enters the subsonic region. This makes accurately predicting the ballistic behaviour of bullets in the transonic region very hard. Because of this marksmen normally restrict themselves to engaging targets within the supersonic range of the bullet used. ## Testing the predictive qualities of softwareDue to the practical inability to know in advance and compensate for all the variables of flight, no software simulation, however advanced, will yield predictions that will always perfectly match real world trajectories. It is however possible to obtain predictions that are very close to actual flight behaviour. ## Empirical measurement methodBallistic prediction computer programs intended for (extreme) long ranges can be evaluated by conducting field tests at the supersonic to subsonic transition range (the last 10 to 20 % of the supersonic range of the rifle/cartridge/bullet combination). For a typical .338 Lapua Magnum rifle for example, shooting standard 16.2 gram (250 gr) Lapua Scenar GB488 bullets at 905 m/s (2969 ft/s) muzzle velocity, field testing of the software should be done at â‰ˆ 1200 - 1300 meters (1312 - 1422 yd) under International Standard Atmosphere sea level conditions (air density Ï = 1.225 kg/mÂ³). To check how well the software predicts the trajectory at shorter to medium range, field tests at 20, 40 and 60% of the supersonic range have to be conducted. At those shorter to medium ranges, transsonic problems and hence unbehaved bullet flight should not occur, and the BC is less likely to be transient. Testing the predicative qualities of software at (extreme) long ranges is expensive because it consumes ammunition; the actual muzzle velocity of all shots fired must be measured to be able to make statistically dependable statements. Sample groups of less than 24 shots do not obtain statistically dependable data. ## Doppler radar measurement methodGovernments, professional ballisticians, defence forces and a few ammunition manufacturers can use Doppler radars to obtain precise real world data regarding the flight behaviour of the specific projectiles of their interest and thereupon compare the gathered real world data against the predictions calculated by ballistic computer programs. The normal shooting or aerodynamics enthusiast, however, has no access to such expensive professional measurement devices. Authorities and projectile manufacturers are generally reluctant to share the results of Doppler radar tests and the test derived drag coefficients (C In January 2009 the Finnish ammunition manufacturer Lapua published Doppler radar test-derived drag coefficient data for most of their rifle projectiles. Some of the Lapua-provided drag coefficient data shows drastic increases in the measured drag around or below the Mach 1 flight velocity region. This behaviour was observed for most of the measured small calibre bullets, and not so much for the larger calibre bullets. This implies some (mostly smaller calibre) rifle bullets exhibited coning and/or tumbling in the transonic/subsonic flight velocity regime. The information regarding unfavourable transonic/subsonic flight behaviour for some of the tested projectiles is important. This is a limiting factor for extended range shooting use, because the effects of coning and tumbling are not easily predictable and potentially catastrophic for the best ballistic prediction models and software. It should be noted that presented C ## External factors## WindWind has a range of effects, the first being the effect of making the bullet deviate to the side. From a scientific perspective, the "wind pushing on the side of the bullet" is not what causes wind drift. What causes wind drift is drag. Drag makes the bullet turn into the wind, keeping the centre of air pressure on its nose. This causes the nose to be cocked (from your perspective) into the wind, the base is cocked (from your perspective) "downwind." So, (again from your perspective), the drag is pushing the bullet downwind making bullets follow the wind. A somewhat less obvious effect is caused by head or tailwinds. A headwind will slightly increase the relative velocity of the projectile, and increase drag and the corresponding drop. A tailwind will reduce the drag and the bullet drop. In the real world pure head or tailwinds are rare, since wind seldom is constant in force and direction and normally interacts with the terrain it is blowing over. This often makes ultra long range shooting in head or tailwind conditions difficult. ## Vertical anglesThe vertical angle (or elevation) of a shot will also affect the trajectory of the shot. Ballistic tables for small calibre projectiles (fired from pistols or rifles) assume that gravity is acting nearly perpendicular to the bullet path. If the angle is up or down, then the perpendicular acceleration will actually be less. The effect of the path wise acceleration component will be negligible, so shooting up or downhill will both result in a similar decrease in bullet drop. ## Ambient air densityAir temperature, pressure, altitude and humidity variations make up the ambient air density. Humidity has a counter intuitive impact. Since water vapor has a density of 0.8 grams per litre, while dry air averages about 1.225 grams per litre, higher humidity actually decreases the air density, and therefore decreases the drag. ## Long range factors## Gyroscopic drift (Spin drift)Even in completely calm air, with no sideways air movement at all, a spin-stabilized projectile will experience a spin-induced sideways component. For a right hand (clockwise) direction of rotation this component will always be to the right. For a left hand (counterclockwise) direction of rotation this component will always be to the left. This is because the projectile's longitudinal axis (its axis of rotation) and the direction of the velocity of the center of gravity (CG) deviate by a small angle, which is said to be the equilibrium yaw or the yaw of repose. For right-handed (clockwise) spin bullets, the bullet's axis of symmetry points to the right and a little bit upward with respect to the direction of the velocity vector as the projectile rotates through its ballistic arc on a long range trajectory. As an effect of this small inclination, there is a continuous air stream, which tends to deflect the bullet to the right. Thus the occurrence of the yaw of repose is the reason for bullet drift to the right (for right-handed spin) or to the left (for left-handed spin). This means that the bullet is "skidding" sideways at any given moment, and thus experiencing a sideways component. The following variables affect the magnitude of gyroscopic drift: - Projectile or bullet length: longer projectiles experience more gyroscopic drift because they produce more lateral "lift" for a given yaw angle.
- Spin rate: faster spin rates will produce more gyroscopic drift because the nose ends up pointing farther to the side.
- Range, time of flight and trajectory height: gyroscopic drift increases with all of these variables.
Doppler radar measurement results for the gyroscopic drift of several US military and other very-low-drag bullets at 1000 yards (914.4 m) look like this:
The table shows that the gyroscopic drift is rather variable and no clear trend is easily distinguishable. ## Magnus effectSpin stabilized projectiles are affected by the Magnus effect, whereby the spin of the bullet creates a force acting either up or down, perpendicular to the sideways vector of the wind. In the simple case of horizontal wind, and a right hand (clockwise) direction of rotation, the Magnus effect induced pressure differences around the bullet cause a downward force to act on the projectile, affecting its point of impact. ## Magnus effect and bullet stabilityThe Magnus effect has a significant role in bullet stability because the Magnus force does not act upon the bullet's center of gravity, but the center of pressure affecting the Paradoxically, very-low-drag bullets due to their length have a tendency to exhibit greater Magnus destabilizing errors because they have a greater surface area to present to the oncoming air they are travelling through, thereby reducing their aerodynamic efficiency. This subtle effect is one of the reasons why a calculated C ## Poisson effectAnother minor cause of drift, which depends on the nose of the projectile being above the trajectory, is the Poisson Effect. This, if it occurs at all, acts in the same direction as the gyroscopic drift and is even less important than the Magnus effect. It supposes that the uptilted nose of the projectile causes an air cushion to build up underneath it. It further supposes that there is an increase of friction between this cushion and the projectile so that the latter, with its spin, will tend to roll off the cushion and move sideways. This simple explanation is quite popular. There is, however, no evidence to show that increased pressure means increased friction and unless this is so, there can be no effect. Even if it does exist it must be quite insignificant compared with the gyroscopic and Coriolis drifts. Both the Poisson and Magnus Effects will reverse their directions of drift if the nose falls below the trajectory. When the nose is off to one side, as in equilibrium yaw, these effects will make minute alterations in range. ## Coriolis driftThe Coriolis effect causes drift related to the spin of the Earth, known as Coriolis drift. Coriolis drift can be up, down, left or right. Coriolis drift is not an aerodynamic effect. It is a result of flying from one point to another across the surface of a rotating sphere (Earth). For small arms, this effect is generally insignificant, but for ballistic projectiles with long flight times, such as extreme long-range rifle projectiles, artillery and intercontinental ballistic missiles, it is a significant factor in calculating the trajectory. The coordinate system that is used to specify the location of the point of firing and the location of the target is the system of latitudes and longitudes, which is in fact a rotating coordinate system, since the Earth is a rotating sphere. During its flight, the projectile moves in a straight line (not counting gravitation and air resistance for now). Since the target is co-rotating with the Earth, it is in fact a moving target, relative to the projectile, so in order to hit it the gun must be aimed to the point where the projectile and the target will arrive simultaneously. When the straight path of the projectile is plotted in the rotating coordinate system that is used, then this path appears as curvilinear. The fact that the coordinate system is rotating must be taken into account, and this is achieved by adding terms for a "centrifugal force" and a "Coriolis effect" to the equations of motion. When the appropriate Coriolis term is added to the equation of motion the predicted path with respect to the rotating coordinate system is curvilinear, corresponding to the actual straight line motion of the projectile. For an observer with his frame of reference in the northern hemisphere Coriolis makes the projectile appear to curve over to the right. Actually it is not the projectile swinging to the right but the earth (frame of reference) rotating to the left which produces this result. The opposite will seem to happen in the southern hemisphere. The direction of Coriolis drift depends on the firer's location or latitude on the sphere, and the azimuth of firing. The magnitude of the drift depends on the location, azimuth, and time of flight. The Coriolis effect is at its maximum at the poles and negligible at the equator of the Earth. The reason for this is that the Coriolis effect depends on the vector of the angular velocity of the Earths rotation with respect to xyz - coordinate system (frame of reference). ## Equipment factorsThough not forces acting on projectile trajectories there are some equipment related factors that influence trajectories. Since these factors can cause otherwise unexplainable external ballistic flight behaviour they have to be briefly mentioned. ## Lateral jumpLateral jump is caused by a slight lateral and rotational movement of a gun barrel at the instant of firing. It has the effect of a small error in bearing. The effect is ignored, since it is small and varies from round to round. ## Lateral throw-offLateral throw-off is caused by mass imbalance in applied spin stabilized projectiles or pressure imbalances during the transitorily flight phase when a projectile leaves a gun barrel. If present it causes dispersion. The effect is unpredictable, since it is generally small and varies from projectile to projectile, round to round and/or gun barrel to gun barrel. ## Maximum effective small arms rangeThe maximum practical range - ballistic coefficient of the bullets used
- height of the sighting components above the rifle bore axis
- the zero range at which the sighting components and rifle combination were sighted in
- bullet weight
- actual muzzle velocity (powder temperature affects muzzle velocity, primer ignition is also temperature dependent)
- range to target
- supersonic range of the employed gun, cartridge and bullet combination
- inclination angle in case of uphill/downhill firing
- target speed and direction
- wind speed and direction (main cause for horizontal projectile deflection and generally the hardest ballistic variable to measure and judge correctly. Wind effects can also cause vertical deflection.)
- air temperature, pressure, altitude and humidity variations (these make up the ambient air density)
- earth's gravity (changes slightly with latitude and altitude)
- gyroscopic drift (horizontal and vertical plane gyroscopic effect â€” often know as spin drift - induced by the barrels twist direction and twist rate)
- coriolis effect drift (latitude, direction of fire and hemisphere data dictate this effect)
- lateral throw-off (dispersion that is caused by mass imbalance in the applied projectile)
- aerodynamic jump (dispersion that is caused by lateral (wind) impulses activated during free flight at or very near the muzzle)
^{[21]} - the inherent potential accuracy and adjustment range of the sighting components
- the inherent potential accuracy of the rifle
- the inherent potential accuracy of the ammunition
- the inherent potential accuracy of the computer program and other firing control components used to calculate the trajectory
The ambient air density is at its maximum at Arctic sea level conditions. Cold gunpowder also produces lower pressures and hence lower muzzle velocities than warm powder. This means that the maximum practical range of rifles will be at it shortest at Arctic sea level conditions. The ability to hit a target at great range has a lot to do with the ability to tackle environmental and meteorological factors and a good understanding of exterior ballistics and the limitations of equipment. Without computer support and highly accurate laser rangefinders and meteorological measuring equipment as aids to calculate ballistic solutions, long-range shooting beyond 1000 m (1100 yd) becomes guesswork for even the most expert long-range marksmen.
## Using ballistics dataHere is an example of a ballistic table for a .30 calibre Speer 169 grain (11 g) pointed boat tail match bullet, with a BC of 0.480. It assumes sights 1.5 inches (38 mm) above the bore line, and sights adjusted to result in point of aim and point of impact matching 200 yards (183 m) and 300 yards (274 m) respectively.
This table demonstrates that, even with a fairly aerodynamic bullet fired at high velocity, the "bullet drop" or change in the point of impact is significant. This change in point of impact has two important implications. Firstly, estimating the distance to the target is critical at longer ranges, because the difference in the point of impact between 400 and 500 yd (460 m) is 25-32 in (depending on zero), in other words if the shooter estimates that the target is 400 yd away when it is in fact 500 yd away the shot will impact 25-32 in (635-813 mm) below where it was aimed, possibly missing the target completely. Secondly, the rifle should be zeroed to a distance appropriate to the typical range of targets, because the shooter might have to aim so far above the target to compensate for a large bullet drop that he may lose sight of the target completely (for instance being outside the field of view of a telescopic site). In the example of the rifle zeroed at 200 yd (180 m), the shooter would have to aim 49 in or more than 4 ft (1.2 m) above the point of impact for a target at 500 yd. ## Freeware small arms external ballistics software- GNU Exterior Ballistics Computer (GEBC) - An open source 3DOF ballistics computer for Windows, Linux, and Mac - Supports the G1, G2, G5, G6, G7, and G8 drag models.
- Nerdulator.net Exterior Ballistics Computer - A web-based small arms ballistics interface based on the open source GNU Exterior Ballistics Library, originally written by Derek Yates - Supports the G1 and G8 drag models.
- 6mmbr.com ballistics section links to / hosts 4 freeware external ballistics computer programs.
- 2DOF & 3DOF R.L. McCoy - Gavre exterior ballistics (zip file) - Supports the G1, G2, G5, G6, G7, G8, GS, GL, GI, GB and RA4 drag models
- PointBlank Ballistics (zip file) - Siacci/Mayevski G1 drag model
- Remington Shoot! A ballistic calculator for Remington factory ammunition (based on Pinsoft's Shoot! software). - Siacci/Mayevski G1 drag model
- JBM's small-arms ballistics calculators Online trajectory calculators - Supports the G1, G2, G5, G6, G7, G8, GI and GL drag models.
- Pejsa Ballistics (MS Excel spreadsheet) - Pejsa model
- Sharpshooter Friend (Palm PDA software) - Pejsa model
## Evaluation small arms external ballistics software- Lex Talus Corporation "Precision Shooter's WorkbenchÂ©" and "Field Firing SolutionsÂ©" fully functional 30-day free evaluation programs for Windows and PDA - Pejsa model
- Gen(X)apps "BallistiX" fully functional time limited evaluation program for Windows and MAC using US customary units - Pejsa model
## See also- Internal ballistics - The behaviour of the projectile and propellant before it leaves the barrel.
- Terminal ballistics - The behaviour of the projectile upon impact with the target.
- Trajectory of a projectile - Basic external ballistics mathematic formulas.
## References**^**Ballistic Coefficients Do Not Exist! By Randy Wakeman**^**Weite SchÃ¼sse - drei (German)**^**Historical Summary**^**LM Class Bullets, very high BC bullets for windy long Ranges**^**.338 Lapua Magnum product brochure from Lapua**^**300 grs Scenar HPBT brochure from Lapua**^**Pejsa Ballistics**^**Lex Talus Corporation Pejsa based ballistic software**^**Patagonia Ballistics Pejsa based ballistic software**^**Most spin stabilized projectiles that suffer from lack of dynamic stability have the problem near the speed of sound where the aerodynamic forces and moments exhibit great changes. It is less common (but possible) for bullets to display significant lack of dynamic stability at supersonic velocities. Since dynamic stability is mostly governed by transonic aerodynamics, it is very hard to predict when a projectile will have sufficient dynamic stability (these are the hardest aerodynamic coefficients to calculate accurately at the most difficult speed regime to predict (transonic)). The aerodynamic coefficients that govern dynamic stability: pitching moment, Magnus moment and the sum of the pitch and angle of attack dynamic moment coefficient (a very hard quantity to predict). In the end, there is little that modelling and simulation can do to accurately predict the level of dynamic stability that a bullet will have downrange. If a bullet has a very high or low level of dynamic stability, modelling may get the answer right. However, if a situation is borderline (dynamic stability near 0 or 2) modelling cannot be relied upon to produce the right answer. This is one of those things that have to be field tested and carefully documented.**^**Lapua Bullets Drag Coefficient Data for QuickTARGET Unlimited**^**Lapua bullets CD data (zip file)**^**Nenstiel Yaw of repose**^**Gyroscopic Drift and Coreolis Acceleration by Brian Litz**^**Nenstiel The Magnus effect**^**Nenstiel The Magnus force**^**Nenstiel The Magnus moment**^**Gyroscopic Drift and Coreolis Acceleration by Bryan Litz**^**The snipershide website defines effective range as: The range in which a competent and trained individual using the firearm has the ability to hit a target sixty to eighty percent of the time. In reality, most firearms have a true range much greater than this but the likely-hood of hitting a target is poor at greater than effective range. There seems to be no good formula for the effective ranges of the various firearms.**^**The US Army Research Laboratory did a study in 1999 on the practical limits of several sniper weapon systems and different methods of fire control. Sniper Weapon Fire Control Error Budget Analysis - Raymond Von Wahlde, Dennis Metz, August 1999**^**The Effects of Aerodynamic Jump Caused by a Uniform Sequence of Lateral Impulses - Gene R. Cooper, July 2004**^**An example of how accurate a long-range shooter has to establish sighting parameters to calculate a correct ballistic solution is explained by these test shoot results. A .338 Lapua Magnum rifle sighted in at 300 m shot 250 grain (16.2 g) Lapua Scenar bullets at a measured muzzle velocity of 905 m/s. The air density Ï during the test shoot was 1.2588 kg/mÂ³. The test rifle needed 13.2 mils (45.38 MOA) elevation correction from a 300 m zero range at 61 degrees latitude (gravity changes slightly with latitude) to hit a human torso sized target dead centre at 1400 m. The ballistic curve plot showed that between 1392 m and 1408 m the bullets would have hit a 60 cm (2 ft) tall target. This means that if only a 0.6% ranging error was made a 60 cm tall target at 1400 m would have been completely missed. When the same target was set up at a less challenging 1000 m distance it could be hit between 987 m and 1013 m. This makes it obvious that with increasing distance apparently minor measuring and judgment errors become a major problem.
## External links
- Tan, A., Frick, C.H., and Castillo, O. (1987). "The fly ball trajectory: An older approach revisited".
*American Journal of Physics***55**(1): 37. doi: . (Simplified calculation of the motion of a projectile under a drag force proportional to the square of the velocity) - "The Perfect Basketball Shot".
*(PDF)*. http://www.wooster.edu/physics/jris/Files/Satti.pdf. Retrieved on September 26 2005. - basketball ballistics.
- Speer Reloading Manual Number 11, Omark Industries, 1987 (no ISBN)
- How do bullets fly? by Ruprecht Nennstiel, Wiesbaden, Germany
- Exterior Ballistics.com
- A Short Course in External Ballistics
- Articles on long range shooting by Bryan Litz
- How External Ballistics Programs Work by Bryan Litz
- 2DOF and 3DOF Exterior Ballistics in MS Excel by Hans Cronander, Goteburg, Sweden
- Website of Pejsa Ballistics
- Weite SchÃ¼sse - part 4, Basic explanation of the Pejsa model by Lutz MÃ¶ller (German)
- Patagonia Ballistics ballistics mathematical software engine
- BRITISH ARTILLERY FIRE CONTROL - BALLISTICS & DATA
- FIELD ARTILLERY, VOLUME 6, BALLISTICS AND AMMUNITION
Source: Wikipedia, the free encyclopedia
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