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# spin drift & Coriolis effect

#22
03-20-2011, 11:53 PM
 Bronze Member Join Date: Feb 2011 Posts: 46
Re: spin drift & Coriolis effect

Quote:
 Originally Posted by Imho 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.

#23
03-21-2011, 12:49 AM
 Junior Member Join Date: Mar 2011 Posts: 19
Re: spin drift & Coriolis effect

Quote:
 Originally Posted by rscott5028 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.
Although your reasoning seems logical, the actual forces at work result in the opposite effect.

People quite commonly refer to the Coriolis Effect when talking about two separate effects, the actual Coriolis Effect and the Eötvös Effect.

At the risk of over simplifying things, the Coriolis Effect refers to the projectile (seemingly) deflecting horizontally and the Eötvös Effect refers to the projectile deflecting vertically.

In short, the Eötvös Effect results in Eastward moving objects having less gravitational force applied over their journey (in the case of a projectile the POI will therefore be high in relation to the POA), and Westward moving objects having more gravitational force applied (and therefore the POI will be low in relation to the POA).

I'm no expert, so I hope I've explained this correctly. The actual mechanics behind the "forces" at work really does my head in.

Just knowing that these factors exist is probably enough for most. Leave the mechanics to the physicists and actual values to ballistic software.

Quote:
 Originally Posted by rscott5028 Fortunately, we have computers and lots of gadgets to help us account for this.
Exactly.
#24
03-21-2011, 12:04 PM
 Platinum Member Join Date: Apr 2010 Location: Allen, TX Posts: 2,608
Re: spin drift & Coriolis effect

Yes. I had my wires crossed.

Bryan's website has a great explanation and he's the expert.
spindrift
#25
03-21-2011, 08:43 PM
 Silver Member Join Date: Jan 2010 Location: utah Posts: 366
Re: spin drift & Coriolis effect

Quote:
 Originally Posted by Bravo 4 So was this supposed to say you add 3" right for Spin Drift and another 3" right for Coriolis? If so, I hate to tell you this but you cannot just put a number on Coriolis like you can Spin Drift because it is never gonna be constant...unless you are shooting at the same range (and I don't mean range as in distance, I mean range as in Firing Range/shooting spot). 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.
actually it does alway cause an impact right unless you are in the southern hemisphere in which it will ALLWAYS be LEFT. just as a left spin will cause left drift.
if you dont beleave me shoot out to 1760 yrds and do as you describe. you WILL be WAY off if you try to adjust for a impact left corialis in the northern hemisphere no matter the direction u shoot.

the adjustments i list will get u closer than u can dial anywere in the usa(except alaska), given mean velocity of 2800 fps (a good median for most types of rifles)and bc in the high 5's

Last edited by load; 03-21-2011 at 08:48 PM..
#26
03-21-2011, 11:11 PM
 Bronze Member Join Date: Feb 2011 Posts: 46
Re: spin drift & Coriolis effect

i was looking at the link to Applied ballistics the equation for the gravity multiplier accounts for muzzle velocity but not flight time how can it be accurate? if it is going to account for the velocity shouldn't it account for the average velocity. has anyone tried to use this equation with success? either it should account for the velocity and distance or just come up with a gravity multiplier for a direction and longitude. I put the equation into excel and got completely different results. Can someone who is smarter than me tell me what I am doing wrong?

http://www.appliedballisticsllc.com/...files/vert.pdf
#27
03-22-2011, 12:42 AM
 Junior Member Join Date: Mar 2011 Posts: 19
Re: spin drift & Coriolis effect

Once again, I'm no expert, but the way I read the formula it is producing a "multiplier" which his then applied to the (already calculated) effects of gravity in the bullet drop mentioned in the example.
#28
03-22-2011, 01:52 AM
 Junior Member Join Date: Mar 2011 Posts: 19
Re: spin drift & Coriolis effect

In Excel the formula for the cell would be:

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