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Old April 13, 2010, 08:34 PM   #17
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From The Complete Blackpowder Handbook: The Latest Guns and Gear
By Sam Fadala:

Forward velocity is killed by the atmosphere. Gravity plays a role in bullet flight, but it isn't nearly as responsible as the atmosphere for slowing forward progress. Rotational velocity, on the other hand, is much better retained........
........We also recognize by understanding rotational spin retention why the round ball continues to maintain its original attitude in flight to a reasonable distance. Losing 50 per cent of its original velocity within only 100 yards is common.
The Magnus effect is the phenomenon whereby a spinning object flying in a fluid creates a whirlpool of fluid around itself, and experiences a force perpendicular to the line of motion. The overall behaviour is similar to that around an aerofoil (see lift force) with a circulation which is generated by the mechanical rotation, rather than by aerofoil action.

In external ballistics

The critical factor is the location of the centre of pressure, which depends on the flowfield structure, which in turn depends mainly on the bullet's speed (supersonic or subsonic), but also the shape, air density and surface features. If the centre of pressure is ahead of the centre of gravity, the effect is destabilizing; if the centre of pressure is behind the centre of gravity, the effect is stabilizing.

Last edited by arcticap; April 13, 2010 at 08:43 PM.
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