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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Hornady ELD-X bullets
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<blockquote data-quote="Bullseye" data-source="post: 1133278" data-attributes="member: 3351"><p>Again you seem to completely miss the point. This entire discussion by Hornady has nothing to do with BC. The reason they have steered all there technical discussion to Drag coefficient is to get away from the inherent problems and inaccuracy with BC. Any BC drag model. If the projectile shape and the drag coefficient versus Mach number of the projectile you are evaluating does not match the shape and Cd versus Mach of whatever standard you are comparing to you will have errors. End of conversation. G7 in general is a better approximation of a boat tail, modern ogive projectile than G1. Again BC is not the discussion here. The discussion is the fact that current polymer tips, under certain conditions are degrading significantly because of aerodynamic heating and negatively effecting the drag performance in flight. If you look at the drag coefficient plots that Hornady shows this is obvious. It is not gyroscopic stability or limit cycle yaw, or changing BC or any other buzz phrase that somebody wants to throw at the wall and confuse people. You can't create and maintain a yaw condition at the muzzle that is maintained for the entire supersonic flight of a projectile without the bullet becoming totally unstable and tumbling, which from looking at their data it is not. It's not possible without an external disturbance. The differences and change in the BC's as a function of velocity are well known They are a function of how well the standard and the subject bullets drag coefficient match. The change in the BC is gradual and does not happen near as fast or as soon as the drag is changing in Hornady' s data. BC is a simple minded approximation in order to simplify a very complex math problem and provide a simple, approximate way to calculate trajectories, period.</p><p></p><p>You need to re-read McCoy and what the graphs in his book show. The boat tail has a much greater contribution to total drag in the transonic than it does supersonic, Pg. 72. The length and shape of the ogive and the size of the meplat, the point, are the overwhelming contributors to supersonic drag, Pg. 70 and 71. Put a boat tail on a round nose and it still has terrible aerodynamics. That's why if you look at the plots you will see the conventional tipped bullet rapidly depart from the new tip from the muzzle and then the two beginning to come back together at low supersonic mach numbers.</p></blockquote><p></p>
[QUOTE="Bullseye, post: 1133278, member: 3351"] Again you seem to completely miss the point. This entire discussion by Hornady has nothing to do with BC. The reason they have steered all there technical discussion to Drag coefficient is to get away from the inherent problems and inaccuracy with BC. Any BC drag model. If the projectile shape and the drag coefficient versus Mach number of the projectile you are evaluating does not match the shape and Cd versus Mach of whatever standard you are comparing to you will have errors. End of conversation. G7 in general is a better approximation of a boat tail, modern ogive projectile than G1. Again BC is not the discussion here. The discussion is the fact that current polymer tips, under certain conditions are degrading significantly because of aerodynamic heating and negatively effecting the drag performance in flight. If you look at the drag coefficient plots that Hornady shows this is obvious. It is not gyroscopic stability or limit cycle yaw, or changing BC or any other buzz phrase that somebody wants to throw at the wall and confuse people. You can’t create and maintain a yaw condition at the muzzle that is maintained for the entire supersonic flight of a projectile without the bullet becoming totally unstable and tumbling, which from looking at their data it is not. It’s not possible without an external disturbance. The differences and change in the BC’s as a function of velocity are well known They are a function of how well the standard and the subject bullets drag coefficient match. The change in the BC is gradual and does not happen near as fast or as soon as the drag is changing in Hornady’ s data. BC is a simple minded approximation in order to simplify a very complex math problem and provide a simple, approximate way to calculate trajectories, period. You need to re-read McCoy and what the graphs in his book show. The boat tail has a much greater contribution to total drag in the transonic than it does supersonic, Pg. 72. The length and shape of the ogive and the size of the meplat, the point, are the overwhelming contributors to supersonic drag, Pg. 70 and 71. Put a boat tail on a round nose and it still has terrible aerodynamics. That’s why if you look at the plots you will see the conventional tipped bullet rapidly depart from the new tip from the muzzle and then the two beginning to come back together at low supersonic mach numbers. [/QUOTE]
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