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World record rifle shot
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WYDave
Posted 9/25/2022 00:11 (#9859874 - in reply to #9857946)
Subject: RE: World record rifle shot


Wyoming

My ballistics book gives the following formula:

coriolis deflection[*] in feet = 0.000072722 * distance(in feet) * sin(latitude in degrees) * time of flight(in seconds)

Again, working with a latitude of 43 degrees for that approximate area of Wyoming, and 24 seconds for time of flight, we get:

0.000072722 * 22,965 feet * sin(43 degrees) * 24 = 27.3 feet (approximately) to the right.

[*] In the northern hemisphere, your deviation will be to the right. In the southern hemisphere, it will be to the left.

 

At 1,000 yards at the same latitude, it would look like this if we were launching a Berger 175 grain boattail .308 match bullet with a muzzle velocity of 2400 fps:

0.000072722 * 3,000 feet * sin(43) * 1.847 seconds = 0.2748 feet to the right. We're talking 3.mumble inches.

I'm simplifying things by not taking into account air density, altitude, humidity, etc, etc. I'm just using standard values.

What's really magnifying their issue is their shot's hang time. They had to loft their shot so far above the line-of-sight to the target, the bullet is hanging in the air for 24 seconds. It takes less than two seconds for a common .308 match bullet to get to 1,000 yards when launched at modest velocity - but here's what is happening in their scenario: Most rifle rounds run out of gas somewhere at about 1700 yards and go sub-sonic. Now things slooooooow down... theirs was probably supersonic out to at least 2500 yards, but their velocity at impact was less than 700 fps. They've bled off the majority of their velocity - and now that bullet is hanging in the air far, far longer than most shots.

For most bullets, as the bullet slows down towards the sound barrier (they started out supersonic and the bullet drops through the sound barrier), the bullet's drag is going up. When the bullet comes down through the transsonic region, the drag suddenly drops, and the bullet can amble on towards the target, but it is now taking much longer to get there.

There is something else that has to be taken into account at long ranges called "spin drift," that is either a right drift (for right-hand twist barrels) or left (for left-hand twist barrels), and for the 1,000 yard shooter, swamps consideration of the Coriolis effect.

 

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