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Long Range shots - elevation right on always to the right

 
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  #36  
Old 08-25-2011, 01:10 PM
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Re: Long Range shots - elevation right on always to the right

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Originally Posted by fatrack View Post
Hey Phorwath,

I'm thinking about the Coriolis effect-

In regard to a shot along a North or South trajectory, my gut tells me the target would "move away" from the aim point faster than an East-West shot. I would even be inclined to think a East-West shot (small arms) should have negligible effect because the target is moving almost directly towards or away from the origin of fire.

Can you post a Coriolis correction for a shot fired either N-S at 45 latitude for comparison to the E-W correction you gave? Interesting stuff!
As the graphic I posted shows the target does not remain constant relative to the line of flight of the bullet on such a shot. I've always however been taught that at the ranges we are talking about it's simply negligible.

I'm beginning to wonder if the program he's using calculates some affect on the actual flight of the bullet relative to something akin to centrifugal force which I've not ever considered.

If you think about a spinning ball if you drop a little water on it's top axis the water will naturally gravitate towards the equator and then "spin off" of the ball.

If this is the case I'm actually learning something new for a change because I would have never considered such an effect to have any significance in point of impact.
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  #37  
Old 08-25-2011, 01:14 PM
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Re: Long Range shots - elevation right on always to the right

Quote:
Originally Posted by fatrack View Post
Hey Phorwath,

I'm thinking about the Coriolis effect-

In regard to a shot along a North or South trajectory, my gut tells me the target would "move away" from the aim point faster than an East-West shot. I would even be inclined to think a East-West shot (small arms) should have negligible effect because the target is moving almost directly towards or away from the origin of fire.

Can you post a Coriolis correction for a shot fired either N-S at 45 latitude for comparison to the E-W correction you gave? Interesting stuff!
I thought the same until I spent days researching the topic.

Remember the input parameters here are the OP's 3000 fps MV, and a 200 gr Nosler Accubond bullet with an advertised G1-BC = 0.588.

At 45 degrees North Latitude, the rightward Coriolis Drift is 2.5" at 1000 yds no matter the direction of fire. The horizontal component of Coriolis drift is not dependent on the direction of horizontal fire. You can point your rifle N-S-E-W. NE-SW-NW-SE. The rightward bullet drift due to the Coriolis Effect is 2.5" over the first 1000 yds of bullet travel. Coriolis caused horizontal drift is dependent on Latitude of the shooter, being maximized at the poles and minimized to essentially zero for a shooter at the earth's equator.

Coriolis Drift also causes a vertical component of bullet drift, and the quantity of vertical drift IS dependent on the direction of fire. Vertical drift is maximized with true East and true West directions of fire, and diminishes to zero when the direction of fire is true North or true South. In addition, vertical bullet drift is maximum at the earth's equator, and minimized to basically zero at both poles, even with the directions of fire being due East or due West.
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  #38  
Old 08-25-2011, 01:28 PM
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Re: Long Range shots - elevation right on always to the right

Quote:
Originally Posted by WildRose View Post
I'm beginning to wonder if the program he's using calculates some affect on the actual flight of the bullet relative to something akin to centrifugal force which I've not ever considered.

If you think about a spinning ball if you drop a little water on it's top axis the water will naturally gravitate towards the equator and then "spin off" of the ball.
The centripetal force created due to the earth's rotation is a major force causing Coriolis bullet drift.

Believe me, this is not an easy topic to get your head around. I'm an engineer by training and profession. I've had a lot of math, calculus, differential equations, and even an entry level finite element course(s) in college - but that was many years ago. It took me days of research to come to a reasonable comfort level with my understanding of Coriolis effect-caused bullet drift involving small arms fire. I don't proclaim to be knowledgeable enough to teach it. I believe I understand the phenomena well enough to be able to recognize when I should, and shouldn't, be concerned about adding dope in order to account for Coriolis drift for long range shots.

Last edited by phorwath; 08-25-2011 at 01:58 PM.
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  #39  
Old 08-25-2011, 03:09 PM
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Re: Long Range shots - elevation right on always to the right

Phorwath,

So the output from your ballistic program shows the same correction regardless of direction of fire? It is my understanding that programs with a correction for Coriolis have an input for bearing and I would wonder why they have this if it makes no difference on the correction?
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  #40  
Old 08-25-2011, 03:55 PM
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Re: Long Range shots - elevation right on always to the right

Twist your scope so that it tracks with the windage, Horizontal level is wrong for your rifle barrel. Leveling off of the action doesn't mean a thing, but is a good place to start.
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  #41  
Old 08-25-2011, 06:02 PM
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Re: Long Range shots - elevation right on always to the right

All of this bull **** over a screwy scope, come on now guys, its pretty freaking simple, the scope is a piece of ****, tracking wise, send it back and get a replacement that will dial properly.
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  #42  
Old 08-25-2011, 06:43 PM
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Re: Long Range shots - elevation right on always to the right

Now that is a direct answer,,I almost said that but since you did xxxxxxx2.
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