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spin drift & Coriolis effect

 
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  #15  
Old 03-16-2011, 10:53 PM
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Re: spin drift & Coriolis effect

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Originally Posted by Bravo 4 View Post
Yes, it does depend on the direction you are shooting in conjuntion to true north/south. It will not always make your bullet drift right like spin drift from a right hand twist barrel. I believe the the poster below didn't quite catch onto your question.
It was my impression that Coriolis will have the same right component for any given direction but the vertical component changes with direction of fire.

I've found taking drift and Coriolis into account to be very beneficial for my wind calls now that I base it on what's actually going on not chasing "noise".
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  #16  
Old 03-16-2011, 11:03 PM
rem rem is offline
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Re: spin drift & Coriolis effect

I do agree with all of you that all of the little things add up. and i personal wont take a cold bore shot at an animal that I don't know I can make. If you can hit a 10 area at 1000 yards the first time you are the man! my point was based on a gun that shoots 1Moa counting for .25 moa seems silly but if you know what it is then by all means account for it. there are so many conflicting pieces of info on the subject I don't know were to start, except for shooting at all ranges and writing down the results. theory is one thing results are another.
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  #17  
Old 03-17-2011, 01:01 AM
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Re: spin drift & Coriolis effect

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Originally Posted by bigngreen View Post
It was my impression that Coriolis will have the same right component for any given direction but the vertical component changes with direction of fire.

I've found taking drift and Coriolis into account to be very beneficial for my wind calls now that I base it on what's actually going on not chasing "noise".
I believe you are correct.

In the northern hemisphere, the shift in POI due to coriolis will apparently be to the right regardless of whether you are shooting northbound or southbound. This seems counter-intuitive to me. But, here's my understanding...

When you face south, the gun and the bullet are travelling right to left which will "fling" the bullet to the left. However, the target to the south is closer to the equator and will travel from your right to left faster than the bullet is being "flung". Hence, you will end up hitting to the right of your POA.

Conversely when shooting north, the target will be moving from your left to right, but not as fast as the gun/bullet originating closer to the equator and thus being "flung" from left to right faster than the target is moving. As such, you will again hit to the right of your POA.

NOTE: The following 2 statements are incorrect as you'll see if you read subsequent posts...
Shooting westbound, the target will be closer on impact than it was when you squeezed the trigger. So, impact will be higher.

Conversely shooting eastbound, the target will be farther on impact than it was when you squeezed the trigger. So, impact will be lower.

Fortunately, we have computers and lots of gadgets to help us account for this. Whereas, I feel that spin drift may be somewhat more affected by the bullet and individual rifle. No doubt, everyone has an opinion about that.

-- richard

Last edited by rscott5028; 03-21-2011 at 08:05 PM. Reason: comment on erroneuas info...
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  #18  
Old 03-17-2011, 08:00 AM
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Re: spin drift & Coriolis effect

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Originally Posted by rem View Post
....... I don't know were to start, except for shooting at all ranges and writing down the results. theory is one thing results are another.
rem,

That is a great place to "start" and to stick with. I have log books going back over 20 years with my shooting and loading info. Thing is, the longer I play this game the more detailed my log books get. I used to just write down load, weather conditions, and velocity of each round. Now in addition to that, I sketch out groups with each shot numbered (not always but often). I will often make notes of something that did not perform like it should have so I can remind myself and think about it later, etc..... Write down everything..... then refer back to that data, that is where you will learn the most, not when you are actually on the range.

I used to ignore spin drift and coriolis in my calculations and "dope". However, from real world experience I was quite well aware that the further out I shot the more my groups drifted to the right. At 1000 yards I would be about 1/2 to 3/4 moa right. I knew this and compensated for it even when shooting critters at those distances, so even though I did not understand WHY it was happening, my log book assured me it WAS happening so I compensated for it.

After reading Bryan Litz's book on ballistics it dawned on me that the advice I had been using of "spin drift and coriolis are too small to matter" was BAD advice, so now I calculate and compensate for both.

There is no substitute for range time, but make sure you are LEARNING something with your range time, otherwise you are just burning powder....
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  #19  
Old 03-17-2011, 08:18 AM
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Re: spin drift & Coriolis effect

Bravo4,

right yeah, cori is different for different coordinates and range.

Per my classes yeah it's looking to be well received and desired by many shooters. It's come to where I getting a website together so they're probably going to be a consistent thing.

This is a great topic! Thanks,
Tres
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  #20  
Old 03-20-2011, 08:16 PM
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Re: spin drift & Coriolis effect

For those who want a relatively simple explanation of the Coriolis Effect, try THIS link.

Unfortunately, like most complex subjects, the explanation may raise more questions than it answers.

The net effect in terms of impact changes is actually a combination of multiple factors, even when facing directly North/South or East/West.
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  #21  
Old 03-20-2011, 10:04 PM
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Re: spin drift & Coriolis effect

Here's another resource for spin drift and coriolis effect:
spindrift
-Bryan
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