Figure 2 shows this in a greatly exaggerated depiction.Īs I said above, as the bullet flies downrange, the stability steadily increases and so does the yaw of repose. Any spin-stabilized projectile fired from a right-hand twist flies with the nose slightly above and to the right of its line of flight. The first is a direct result of a spin-stabilized projectile. This increase in stability will play a prominent role in spin drift at long ranges. The projectile becomes steadily more and more stable. As the bullet flies downrange and relatively rapidly loses its velocity, the spin rate hardly changes. There is very little that causes the projectile’s spin rate to decrease. Before we get into the specifics of spin drift, we have to have a short discussion on projectile stability.Īs a projectile travels downrange, its stability or resistance to changing its orientation steadily increases. Spin drift is an effect that is another by-product of a spinning, gyroscopically stabilized projectile. If there is a down draft, the projectile will jump to the left. If you fire your rifle and the projectile passes over a cliff or ledge into free air but experiences an updraft of wind at the edge, according to the right-hand rule, the projectile will jump to the right. This response of the projectile can also be a factor when shooting in the mountains while shooting off a ledge or cliff. You can rotate your hand to get different directions of force input and reaction. Practice this for a few minutes because we will be using the right-hand rule to illustrate several of the long-range shooting effects. Your thumb then shows the direction of the response of the projectile to the force input. Your middle finger represents the direction of a force input to the projectile. Your index finger represents the projectile and points in the direction of travel of the projectile. Put your right hand in the configuration shown. This is easy to visualize by using your right hand to show what is called the right-hand rule (see Figure 1). In particular, any gyroscopically stabilized object will respond to an external force 90 degrees to the direction of the input force. The principle side effect that shooters are concerned with is that gyroscopically stabilized objects have some nonintuitive responses to outside forces. This gyroscopic stability is a wonderful thing physics has provided us shooters, but as in most things in life, it comes with side effects. It is the resistance of a rotating body to a change in its orientation. This gyroscopic effect is what gives an otherwise aerodynamically unstable projectile stability, preventing it from tumbling in flight. A spin-stabilized projectile is a rapidly spinning object that for all practical purposes is a gyroscope and will behave like a gyroscope. There is a reality of physics that has to be understood to visualize many of the physical things that happen to a projectile in long-range flight. Most of the calculations of effects were done with the Hornady 4DOF ballistics solver with a Sierra 168-grain MatchKing projectile. Let’s explore each one of these effects, why they occur and just how much impact they have. But how many of us know what the magnitude of these effects are and physically why they occur? We have all heard the shooting and trajectory considerations that have to be made for long-range shooting: muzzle jump, spin drift and Coriolis Effect (what I like to call earth-based effects). Long-range shooting of 1,000 yards to ranges of well over a mile is all the rage today, and manufacturers are putting huge resources into marketing and development of everything long range.īut technology is only as good as the shooter’s knowledge of the ballistics impacting every pull of the trigger.
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