Wind Deflection

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posted on March 3, 2014
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Q: I have heard high-velocity .22 LR bullets are affected by crosswinds to a greater degree than bullets from standard-velocity rounds. This is claimed to be so even though the bullet is in the air for a shorter time and so is affected by the moving air for a shorter time. How can this be?

A: Many strange effects occur when an object nears and exceeds the speed of sound. In the case of .22 LR bullets, the important factor is the greatly increased air resistance at the speed of sound.

A standard-velocity .22 bullet started at a velocity of 1,145 fps takes 0.287 second to travel 100 yards. It could cover the same distance in 0.262 second in a vacuum. The resistance of air delays it 0.025 second. A high-velocity bullet at 1,335 fps muzzle velocity takes 0.259 second to cover the same distance. It could make the trip in 0.225 second in a vacuum, so its delay is 0.034, about 37 percent greater than the standard-velocity bullet. Accordingly, wind deflection is also about 37 percent greater.

This effect, which is pretty well limited to the .22 rimfires, occurs because air resistance increases at a very rapid rate near the speed of sound. Centerfire rifle rounds aren't affected so much because, although air resistance always increases with increased velocity, the rate of increase isn't as steep once the sound barrier has been broken.

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