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Hello Harry,
As John said, initial yaw is largely a function of bullet imbalance. Within the barrel, a projectile is constrained to rotate about its "center of form". Once the projectile leaves the barrel, it is free to rotate about its "center of mass".
If the center of mass does not lie exactly on the center of form, the projectile is unbalanced. An unbalanced projectile will diverge from the axis of the barrel at a "deviation angle" (yaw) that is a function of the radius of gyration (the distance between the center of form and the center of mass) and the twist rate of the barrel.
As an aside, an imperfect bore and/or an imperfect chamber can cause a perfectly balanced projectile to become unbalanced as the projectile moves through the bore.
Given a perfect crown, this deviation angle is the largest contributor to initial yaw. If the crown is less than perfect, it will cause uneven force on the base of the projectile as the projectile leaves the muzzle. These uneven forces will also contribute to initial yaw.
Because of initial yaw, a projectile is strongly influenced by external forces (such as wind) as it leaves the muzzle. The effects you mention are in the class of external forces. These forces can seriously affect downrange performance and are not to be taken lightly.
Jack,
I take your points, but as I have said I also think that there are other factors at work. When ballistics first came to be studied, high speed aerodynamics wasn't understood nor the effects of transiting through the sound barrier in either direction and the shock waves that were set up or changed during flight. It is a factor that is often ignored or of which the shooter has no knowledge of the effects that can be caused.
Harry
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The Lighter Side of Bloop (Read 19130 times)
