Epicyclic Swerve
Here are a couple plots from the simulation showing the pitching and yawing motion of the bullets that were modeled for this project.
This one is the 30 cal 168 gr SMK. I ran the flight conditions McCoy used in Modern Exterior Ballistics: 2600 fps, 1:12 twist, 25 rad/s initial yaw rate. I have about the first 15 to 20 yards of flight here. This was run partly to make sure that I got a pattern for this bullet that's similar to the one that Bob McCoy shows in his book "Modern Exterior Ballistics". The match is perfect.
Second is the 7mm 180 gr Berger VLD at 2820 fps from a 1:9 twist with the same 25 rad/s initial yaw rate for about the first 12-15 yards.
Finally, the same shot for the Berger, only this time out to 110 yards.
Just to be clear about the conclusions of the modeling: The phenomenon of smaller angular groups at longer ranges was not disproven. The only thing I've shown is that if the phenomenon actually happens, epicyclic swerve is not the cause of it.
Here is a video that illustrates the mechanism of epicyclic swerve dynamically
The plot on the left is the angles of the bullets axis (as shown statically above). The plot on the right is the bullets trajectory from the shooters point of view. Notice how small the corkscrew radius is.
Bryan Litz majored in Aerospace Engineering at Penn State University and worked on air-to-air missile design for 6 years in the US Air Force before taking a job as Berger Bullets Chief Ballistician in November 2008. Bryan is now 29 years old, and has been an avid long range shooter since the age of 15. In particular, Bryan enjoys NRA Long Range Prone Fullbore/Palma competition and is the current National Palma Champion. Bryan is also a husband and proud father of 3.
This one is the 30 cal 168 gr SMK. I ran the flight conditions McCoy used in Modern Exterior Ballistics: 2600 fps, 1:12 twist, 25 rad/s initial yaw rate. I have about the first 15 to 20 yards of flight here. This was run partly to make sure that I got a pattern for this bullet that's similar to the one that Bob McCoy shows in his book "Modern Exterior Ballistics". The match is perfect.
Second is the 7mm 180 gr Berger VLD at 2820 fps from a 1:9 twist with the same 25 rad/s initial yaw rate for about the first 12-15 yards.
Finally, the same shot for the Berger, only this time out to 110 yards.
Just to be clear about the conclusions of the modeling: The phenomenon of smaller angular groups at longer ranges was not disproven. The only thing I've shown is that if the phenomenon actually happens, epicyclic swerve is not the cause of it.
Here is a video that illustrates the mechanism of epicyclic swerve dynamically
The plot on the left is the angles of the bullets axis (as shown statically above). The plot on the right is the bullets trajectory from the shooters point of view. Notice how small the corkscrew radius is.
Bryan Litz majored in Aerospace Engineering at Penn State University and worked on air-to-air missile design for 6 years in the US Air Force before taking a job as Berger Bullets Chief Ballistician in November 2008. Bryan is now 29 years old, and has been an avid long range shooter since the age of 15. In particular, Bryan enjoys NRA Long Range Prone Fullbore/Palma competition and is the current National Palma Champion. Bryan is also a husband and proud father of 3.
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