Cross wind effect

If bullets' spin axis points into cross winds, their increased drag means their downrange velocity gets lower. They'll drop more and lose velocity faster.

Ballistic software doesn't show that situation. Downrange drop's the same regardless of wind speed or direction except for the effects of head or tail winds.

Every reloading manual I've looked at has a few errors or myths.
 
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Bart B.

At most a 308 over a 1000 yard flight can only turn 13 minutes off axis, based on the 13 minute uncorrected calculation I ran. If you angle the bullet into the wind, a 175 SMK at 2,600 fps then the correction becomes 10.7 minutes, IIRC.

If Bryan Litze is correct, angling into the center of pressure preserves BC because the bullet is always at its most aerodynamic with reference to the wind stream.

For example a 10 mph crosswind is only 14.5 fps, and when the bullet is traveling 2,600 fps at the muzzle, and over 1,300 fps at 1000, you have a 100 to 1 ratio even when the bullet is traveling the slowest, so the bullet won't angle into the wind enough to see on paper, as 13 minutes is just over 1/8th of a degree, which is probably not enough for any human eye to detect.

If Sierra is correct then the bullet shot angled into the wind eventually "noses over" in the horizontal axis and is pushed back towards the target nose first following the wind. However this would not keep the nose in the center of pressure and would indicate that the nose of the bullet is seeking a path of least resistance.

The difference between the two models, at 1000 yards, is only a bullet orientation of 21.4 minutes (10.7 minutes left and right) of the gun target line. So it isn't a huge difference, although it could be measured with lasers reflecting off the base of the bullet and sensors spread out back at the target line....

Anyone up for writing a physics research grant request?

Jimro
 
BLE,

The football isn't a perfect analogy for a bullet either as it is a symmetrical object (save for the laces) and bullets are not (save for round musket balls), still it is a pretty good analogy as it the ball is spin stabilized and noses over in flight.

Jimro
 
Military folks doing on-site battle damage assement (BDA) have noted that artillery and naval projectiles paths through all sorts of stuff have been the diameter of the rounds. Even though their impact angle was anywhere from zero degrees to the horizontal up to near 90 degrees. Those big projectiles nose over quite easily. Saw some pictures of impact areas 20 miles inland from the battleship New Jersey's 16" guns. Nice and round with a 50+ degree entry angle in that Viet Nam village.
 
BLE,

The football isn't a perfect analogy for a bullet either as it is a symmetrical object (save for the laces) and bullets are not (save for round musket balls), still it is a pretty good analogy as it the ball is spin stabilized and noses over in flight.

Jimro
Click to expand...

Still, it's spin stabilized with the center of mass behind the center of pressure.

Still it amazes me to watch a football thown for a long spiral pass nose over as it changes direction during it's flight.
 
Jimro, a bullet's horizontal trajectory angle from the Line of fire will be greater than the angle from the LOF to the bullets position way down range.

For example, a Palma bullet leaving a .308 at 3000 fps will drift about 81 inches to the left of the line of fire at 1000 yards down range in a 10 mph cross wind from 3 o'clock it's 8.1 MOA left of target center. But it's trajectory axis is about 19 minutes of arc to the left of the line of fire as it moves sideways. It moves sideways about .19 inch for every yard it goes downrange.

From Berger's software:

Rng_____FPS._____Traj______ TOF_______Drift
999_____1430_____0.53_____ 1.4582____-80.89
1000____1428____-0.00_____ 1.4603____-81.08

That bullet is also dropping a bit over 1/2 inch per yard.
 
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Bart B.

You can't take the last yard of a 1000 yard shot and extrapolate a linear trend for the whole shot.

If you did that for drop you would end up calculating that the bullet was falling the whole time.

The reason why the windage correction is less than the total possible movement of the bullet is that for a uniform wind condition you are shooting into the wind, which is blowing it back into the target. If you didn't correct for wind at all the displacement of the bullet would be greater than the correction.

Jimro
 
I only wanted to show the bullet's path at 1000 is a greater angle to the line of fire than the angle from the line of fire is to where the bullet is.

I should have said the line of fire earlier for the angle the bullet is from. The trajectory angle is always greater than the angle from the line of fire to where the bullet's at. The bullet drifted an average of only .081 inch per yard in its flight.

Earlier post was corrected.
 
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