Curvature of the earth?

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bushidomosquito

New member
I was watching the discovery channel and heard about a new rifle by Barret that can reach out to insane distances. They had a balistic calculator that they said can even compensate for the curvature of the earth. Why? How does shooting over a giant sphere affect the bullet path?
 
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Tikirocker

New member
Ah yeah but they need to watch out when they start shooting into toilet bowls in the southern hemisphere ... that stuff will trip Spock out! :rolleyes::D
 
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Musketeer

New member
Stop thinking in 2 dimensions. There is a drop to anything the further away it is from you because the points are on the surface of a sphere. The ground, even on the salt flats out west, is not flat, it is curved. At normal ranges this does not matter but get far enough away and you start to see an effect. At one mile I would think it would be pronounced. How much I cannot be certain without sitting down with calculator and reference texts but I would not be surprised if it was as much as a foot.
 
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model70fan

New member
Correolis effect (I believe it's called), at huge distances the curvature and spin of the earth, and obviously gravity, affect the flight of the bullet
 
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rgitzlaff

New member
Also, don't forget spin drift. The spin of the bullet causes it to drift to the right or left slightly depending on if the rifling is right or left-hand. Yes sir, there are lots of variables to account for in external ballistics. they don't amount to much when you are up close and personall, but when you are reaching way the F-- out there, those variables add up and can mean the difference between a hit and a miss.
 
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30Cal

New member
Spin drift is pretty negligible till well past 1000yds.

If you are standing up, the horizon is at around 5000yds. If your eye is12" off the ground, it's at 2200yds. I'm not sure why someone would think it's really worth compensating for.
 
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Musketeer

New member
Even at 3/4" mentioned above little things add up when making a shot like that. Air density, humidity, temperature, intervening winds. The further you go the more little things come into play. Deciding to just ignore the ones that change POI by an inch will add up quickly.
 
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Musketeer

New member
Watch the making of special on the Shooter DVD. When they start talking about the shooting it is very well done. The explanation of what the round in question does at over a mile when it impacts and why they chose to NOT show that in the film was very interesting. People are ready to see the top of a head blown off but head explosion and torso disassembly as the round actually comes DOWN onto the target is something else entirely
 
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model70fan

New member
Every minute detail is worth compensating for at extreme ranges, 1/4" here, 1/2" there doesn't seem like much at 100 yards, the ranges the OP is talking about by considering the curvature of the earth is a game of hairs, everything that may potentially affect the POI must be considered to have even a remote chance of hitting something at such long ranges with any semblance of consistency. Horizon, mirage, humidity, target location in relation to backdrop (target without a backdrop may seem farther than it is, potentially causing over-compensation for range. Look at most (not all) Easterners hunting the west for the first time, usually shoot over the backs of their first few targets and that is generally only a couple hundred yards) There are many things that people do not consider in long range shooting that are a must for accuracy.
 
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bushidomosquito

New member
Still don't get it. OK, so I guess the curvature thing seems like it might have an effect, except it seems like the bullet drop should be influenced only by gravity and air resistance. Let me put it this way. If I were standing on the ever so slightly curved salt flat shooting through a perfect vaccum in zero gravity at a target one mile away, could I still expect to hit 3/4" low? And spin of the earth:confused: I, my rifle, the ground, the target and air around us are all moving at the same rate so how could that matter. Oh, and let's not forget the fact that the POI changes slightly just by observing the target according to Werner Heizenburg. :D
 
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bcrash15

New member
And spin of the earth I, my rifle, the ground, the target and air around us are all moving at the same rate so how could that matter.
Click to expand...

lets say you were standing at the equator shooting North. If you are to walk around the world east or west, the equator is the longest path you will have to take. If you walk around the world the same way closer to the poles the path is much shorter. So the closer to the equator, the farther that point has to spin to go around once per day, so it must be moving faster to move farther in the same time. Actually, the surface of the earth at the equator is rotating about 1038 mph and nearly 0 around the poles. So when you shoot, your bullet is imparted with the velocity at your latitude, but when shooting north or south, the point your aiming at is rotating at a different rate than the bullet, so your bullet will impact to the side.

I guess basically what this means is that you and your target aren't necessarily moving at the same rate, unless you are shooting directly east-west. This is called the Coriolis effect, and has been known to long range artillery for quite some time.
 
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Jimro

New member
Curve distance verses straight line distance.

We see in straight lines but the surface of the earth isn't a straight line.

The straight line distance is shorter than the curved line distance.

The net force of gravity acts 90 degrees from the surface of the sphere that we call Earth. This means that 3/4's of an inch of "extra gravity" will affect the bullet over the curved line distance of a mile as opposed to the straight line distance.

Hope this helps.

Jimro
 
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jpwilly

New member
No, no thanks, talk about over thinking something. Were going to have to have a computerized scope with laser range finder and radar doppler weather system on it that automatically adjusts the crosshairs for us with all this crap. I'm surprised that we can actually hit a target without a degree. :rolleyes:
 
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5whiskey

New member
Unless your an artillery FDC controller or competing with Carlos H or the Canadian that supposedly tied his record when I was in Afghanistan (that still hasn't been confirmed or denied), you probably don't have to worry about any of this. This is 1000+ yds shooting here folks. I can and hit a target at 1000 yds without compensating for the coriolis effect. If anyone here takes mile long shots then feel free to study it and drop 1200 dollars on a field reliable PDA with proper ballistics software.

I guess the point is this. The wind will play a much larger role than any of this stuff. The wind may be blowing 8 MPH were you are, 3 MPH 500 yds out, and 10 MPH 200 yds from the target. Less than .01% of the GP of shooters MAY dedicate their lives to long range shooting enough to actually be skilled enough in compensating for wind to take shots at 1 mile or more IOT need the formula to calculate the coriolis effect. I am not one of them. If you are then rock on.
 
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Jimro

New member
The Canadian that matched his record wasn't shooting at an individual, he was aiming at a group manning a mortar system and managed to hit one. As such it is not a precision shot as it was against an area target.

Still pretty freakin impressive tho.

Jimro
 
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