THAT explains it...

Discussion in 'General Discussion' started by Albtraum, Oct 30, 2012.

  1. Caneman

    Caneman Active Member

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    not only that, but the pressure creates a wave that moves back and forth from breach to barrel until is dampens, as the wave moves it also affects the diameter of the barrel...
  2. Old Grump

    Old Grump New Member

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    You got it, all this lift silliness is counteracted by the drag of the bullet, a non factor in a vacuum and one nobody seems to be remembering here.

    Bullets have six degrees of dynamic freedom, three translational degrees of freedom and three rotational degrees of freedom. All sporting bullets are spin-stabilized during flight. A flying bullet that is gyroscopically stabilized and trajectories calculated with a three degree of freedom are almost exactly correct. We are only dealing with the three translational degrees of freedom of the bullet, bullet position in downrange, vertical and crossrange coordinates produce a trajectory based on a model that is a point mass with a ballistic coefficient. This is because the spinning bullet is so well stabilized that the rotational motions, other than the spinning motion, are very tiny.

    The small rotation downward pitch of the nose of a bullet as it flies along an arced trajectory stays almost exactly parallel to the velocity vector throughout the trajectory. This motion is caused by a very small aerodynamic sideforce on the bullet resulting from a yaw angle known as the “yaw of repose.” The nose of the bullet is pointed very slightly to the right of the trajectory plane for a bullet of right hand spin, or vice versa for a left hand spin.

    There is a small crossrange deflection of the bullet, to the right for RH spin caused by the tiny aerodynamic sideforce on the bullet resulting from the yaw of repose.

    The bullet turning horizontally to the right or left to follow a crosswind, or turning upward or downward to follow a vertical wind. This turning motion causes a large crossrange deflection of the bullet to follow a crosswind, or a large vertical deflection of the bullet to follow a vertical wind. If you have played with gyroscopes and understand gyroscopic precession you can follow this argument.

    A tiny vertical deflection is caused by a the aerodynamic lift force, or negative lift force, on the bullet, which is necessary to make the bullet turn to follow the crosswind.

    A tiny horizontal deflection of the bullet together with the large vertical deflection, resulting from a vertical wind is caused by a tiny aerodynamic sideforce on the bullet, which makes the bullet turn upward or downward to follow the vertical wind.

    In general they are observable only at longer ranges of 300 yards or more. This is for two reasons. First, as a bullet exits the muzzle with some ballistic yaw, generally an angle near one degree. This yaw causes the bullet to precess, or cone about the velocity vector. As the bullet flies, this coning motion damps out or damps to some minimum value over the first 200 yards. The second reason is that the small effects grow with range flight time. They are overwhelmed by the coning motion at short ranges, but they become observable at longer ranges when the coning motion damps out.

    Is your head hurting yet. This what us old shooters are referring to when we say the bullet goes to sleep. We don't put the good match ammo in the gun till we get to 300 yards or beyond. Up till then a plain old spitzer point flat based bullet will do as well or better at short ranges like 200 yards and under. Now back to the discussion, to make the experiment work you need a vacuum or a dead calm, low humidity, low pressure day and it will be close but not quite the same. Math don't lie but as presented they left out a whole semi trailer full of variables.
  3. aa1911

    aa1911 Active Member

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    someone finally talked about the spin! I was begining to think that was getting ignored.

    I usually love arguments like this, but haven't had enough coffee yet to even add my .02 so I'll leave you guys to it.
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