Bullet Spin
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| Source: http://spectre23.wordpress.com/2009/08/23/sw-22a-shoots-like-a-champ/ |
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Rifling
is the practice where an
arrangement of spiral grooves is cut into the
inside of the barrel of a gun. This causes the
bullet to rotate when it is fired, this
rotation or spin keeps a bullet from tumbling
through the air making for more accurate
shots.  As a bullet travels
through the air its spin will slowly cause it to
travel either to the left or to the right depending on
its direction of rotation, this is referred to as
gyroscopic drift or "spin drift". As a bullet spins clockwise it will slowly
drift to the right, following the same logic if a
bullet spins counterclockwise it will slowly drift to
the left. This is caused by the bullets axis of
rotation and the direction of the velocity vector of
the center of gravity deviating as it spins through
the air. This slight deviation is known
as the yaw of repose. The magnitude of the yaw of
repose is very small making its effect minimal in most
short range situations. This is not the case in a long
distance shot, the longer a shot is the more the spin
of the bullet will affect the trajectory of the shot.
Following this line of logic the farther a bullet
travels the more it will drift either to the left or
right depending on its rotation. Source:http://www.patagoniaballistics.com/images/balengine_clip_image003.jpg Some factors that directly affect the yaw or repose are as follows The length of a bullet The length of a bullet increases the yaw of repose because the longer a bullet is the more lateral lift it produces for any given yaw angle. The spin rate of a bullet As the spin of a bullet increases its left or right gyroscopic drift will increase, the spin rate can also have an affect on a bullet as it travels. If the rotation is to great, a lead or thinly jacketed bullet can be warped and deformed, decreasing accuracy. The air density As air density increases the drift from spin increases. |