Hi, I'm Dr. John Stutz and I teach ballistics to engineers and scientist. Because of the warm welcome, I will continue my series on cool things in external ballistics that you might not know. If you are interested, I have a new bullet design that I am selling called Aerospike Bullets.
So, many of y'all know that spin stabilized bullets "wobble" as they fly. This is called epicyclic motion. An example of the motion of the nose of the bullet is shown below. A bullet is called stable if any disturbance in this motion (like wind or leaving the barrel) decays away and is unstable if it increases. We use what is called the Gyroscopic Stability (Sg) criteria to measure stability. If Sg>1 the bullet is stable and below it is not. There are devices called yaw inducing devices that we use to intentionally cause a large disturbance as the bullet leaves the barrel that exaggerate this motion.
Did you know that there is a second stability criteria? Anyone know what it is?

So, many of y'all know that spin stabilized bullets "wobble" as they fly. This is called epicyclic motion. An example of the motion of the nose of the bullet is shown below. A bullet is called stable if any disturbance in this motion (like wind or leaving the barrel) decays away and is unstable if it increases. We use what is called the Gyroscopic Stability (Sg) criteria to measure stability. If Sg>1 the bullet is stable and below it is not. There are devices called yaw inducing devices that we use to intentionally cause a large disturbance as the bullet leaves the barrel that exaggerate this motion.
Did you know that there is a second stability criteria? Anyone know what it is?
