9 o'clock vs. 3 o'clock wind drifts different with same wind velocity???

[shortpants]

Ok with that exaggerated example that makes sense. It does not quite seem possible ( in my simple mind) that those same effects would happen when applied to a real world shot. Let's say your in WY. shooting facing north. Your bullet impacts right for 2 reasons, 1 your moving to the right and 2 your target is moving left. Simple enough! Now you turn around facing south and shoot the same distance. In this case you and your target are both moving the same direction (left). Are the effects of CE exactly the same? If so why? It seems like the effects would be less in the 2nd shot almost canceling it out. If you can get past the mush between my ears enough to answer that you can take a stab at explaining the effects in an east/west scenario. You've always been a good teacher, I have faith in you!

Post Script:
Hold on a minute!!! It just hit me!!! I miss spoke in the north facing scenario. The target is not moving left (duh) it is moving right but at a slower pace than the shooter. Facing south once again shooter and target are moving the same direction but this time the target is moving faster to the left than the shooter. Is this right? Did I just learn something again! Holy shi+ you guys are making my brain hurt!

Ok but still would like to hear your thoughts on east/west scenario.

 

[Michael Eichele]

East/West senarios result in right hand impact for the northern hemisphere as well. The difference there is it adds a vertical component.

I understand why there is still a right hand impact when firing east and west. Because the earth is round and on an axis, in one way shape or form, the target is either moving or your bullet is moving. The right hand impacts, while slightly different for a given direction of fire, are very close. It is the vertical component that changes the most but is also very minimal (IMHO).

Now it depends also on how near or far you are from the equator. Coriolus effect is seen the least near the equator and the more so the further you get away from it. Mathematically, the coriolus effect is zero on the equator.

 

[ken snyder]

Maybe I have more egg on my face. Now I'm confused again. Pretend I'm a giant WW II cannon on the 45th and I am aiming at a target 50 miles a way to the north, the velocity of the earth where I am at is faster than the velocity of the target so my shell falls to the right. shooting at a target to the south the circumfrance of the earth is bigger and moving faster so my shell falls to the left. Shooting West it hits higher and shooting to the East it hits lower or in front of the target and a North East shot would be basically the same as a crosswind component or a CE component - I don't know

 

[shortpants]

Maybe I have more egg on my face. Now I'm confused again. Pretend I'm a giant WW II cannon on the 45th and I am aiming at a target 50 miles a way to the north, the velocity of the earth where I am at is faster than the velocity of the target so my shell falls to the right. shooting at a target to the south the circumfrance of the earth is bigger and moving faster so my shell falls to the left. Shooting West it hits higher and shooting to the East it hits lower or in front of the target and a North East shot would be basically the same as a crosswind component or a CE component - I don't know

If I'm understanding it right ( and that's a BIG if ) I believe you have it correct except for the part where your shell hits left when shooting south. It would hit right because your target would be moving left at a faster pace than you.

 

[Michael Eichele]

If I'm understanding it right ( and that's a BIG if ) I believe you have it correct except for the part where your shell hits left when shooting south. It would hit right because your target would be moving left at a faster pace than you.

YES!!! You got it!

 

[shortpants]

Ok nobody tell my wife that it is possible for me to learn a new trick! I just finally got her to except that I'm retarded!

 

[Michael Eichele]

I just found an awesome youtube video showing CE. Its over 6 minutes but a darn good example. It shows north/south, south/north launches and east/west, west/east launches and the effects.

[ame=http://www.youtube.com/watch?v=RbJCZaNHTh0&feature=related]Off the sky : Coriolis effect - YouTube[/ame]

 

[SBruce]

Seems that for us here in the northern hemisphere, we're pretty much gauranteed to hit to the right, approx 1-1.25 moa at 1000 yds (combining spin drift and coriolis) assuming dead calm conditions, right hand twist and a zero cant scope mount.

I can see why some of you cant your scopes left by a small amount.
Since it's basically a sure thing, seems that we should take steps to account for it with our sight in or equipment, rather than trying to adjust for it right before the shot.............??

The downside I could foresee in doing that would be the midrange error at 400-600 yds (where most of us are taking LR game at). But I am not sure how much it would be (again, some say they see SD as close as 500 yds). Also, seems that our "left compensation" still wouldn't be enough when we get out to 1500 -1700 yds..........any thoughts?
Of course, most of us aren't expecting a 1st shot connection at beyond 1000 anyway, so maybe a moot point.

 

[paphil]

At the shorter distances, the left hold is much less. at 100 yards,it is 0" ,at 300yards we go up 3 moa from 100 but only left at a percentage(about 1/8 moa) of the 1 moa left at 25 moa at 1000 . At 500 yards I'm up 8 moa but only left about 1/4 moa. The farther we go out the hold gets much bigger. at 1500 yards, I'm up 52 moa so the 1moa hold at 25 moa is now doubled to about 2 moa left and is about 30" . My actual setting is a little less, I try for about 7/8 moa left at 100 yards with 25 moa cranked on the scope, I get a calculated 26" at 1500 yards. I've never used a program that figures spin drift and would be interested to know how close I am at 1500! Once you go past 1000 yards, so many factors come into play that I feel lucky to make any shot. At 2000 yards, 20 degrees temperature change, 1000 feet elevation change, or barometric pressure change of one point from 29 to 30 inches will cause a 60"vertical change in point of impact. Now add in corrielous, spin drift, extreme spread, mirage, incorrect BC's and any number of other factors and shooting at 1000 yards seems much easier, only about 3.5" change for those same variables! Thinking about and being aware of what affects the shot makes you a better shooter! I have a lot of admiration for the snipers making those truely long shots.

 

[Bart B]

Bart, My 6.5-284 is 0'ed at 300 yards and takes exactly 22 moa at 1000 feet elevation and 75 degrees for a 1k shot . It has a BC of .615 with berger bullets and a velocity of 2942 fps.

Forgot to comment on this earlier, so here goes....

If your load needs 22 MOA come up from 300 to zero at 1000, it probably needs 28 to 29 MOA come up from bore sight to zero at a thousand. Therefore, the scope's elevation adjustment axis needs to be rotated about 1.6 degrees left to move the bullet 8 inches horizontally. A 2 degree cant moves the bullet a bit over 10 inches. This assumes your MOA values are the shooter's version of 10 inches per 1000 yards and not the trig version which is 10.47 inches at 1000.

 

[paphil]

I'm just using basic geometry to calculate , I could be wrong. With 22 moa from 300 to 1000, I'll add on 3 more for 0 to 300. Probably not perfect but close enough concidering all the other variables. Now for the basic geometry and math. 25 moa X 1.047"(1moa)= 26.175". Using this as a radius of a circle, 2r X pie= 164.46 " . that is the circumference of the circle. Dividing the circumference by 360 degrees gives us a value for each degree. In this example each degree is worth .456". You are correct that 2 degrees is about 10 inches, .912 to be exact. Without special mounting tools to exactly set the scope, I can't measure 2 degrees. I do know that 1/2 bubble off plumb is about right and I want between 3/4 and 1 inch left of verticle when I crank on 25 moa elevation, it works for me!

 

[Topshot]

While the canted reticle or tilted bubble sounds like an easy solution. And for shots out to 1000 yards, it is.
However spin drift is not linear. You are more likely to get four times the spin drift at 2000 yards than what you get at 1000 yards. So the further you shoot the more care you need to take in working out what's going on. The best way to do this is by actually shooting various distances beyond 1000 yards under perfect conditions to get some real data on whats going on. Unfortunately perfect conditions are not common in a lot of locations. I practiced out past to 2300 yards last week but had to wait for about a month for conditions to be dead calm and suitable.
If I was living in the Northern Hemisphere I would fit my ELR rifles with left twist barrels. Also I find the "Rangecard" app quite handy for getting the bearing of my shots.

 

[Bart B]

I'm just using basic geometry to calculate , I could be wrong. With 22 moa from 300 to 1000, I'll add on 3 more for 0 to 300. Probably not perfect but close enough concidering all the other variables.

It's closer to 6 or 7 MOA, unless you're shooting those bullets out at 5000 fps.

Now for the basic geometry and math. 25 moa X 1.047"(1moa)= 26.175".

That's the trig version. The "shooting" version was established near 100 years ago as exactly 1 inch per 100 yards. 1/3600th of the range. That's why the standard sight radius of competition rifles back then was 30 inches and the rear sight's lead screws at 40 tpi moved 1/3 turn to move the aperture .008333 inch; exactly 1/3600th of the sight radius. And external scope mount bases were 7.2 inches apart; their .002 movement (4 clicks) is also 1/3600th of the spacing.

If one chooses to use trig instead of the shooting version in USA shooting sports venues, they should specificy it.

PS: I built a very accurate optical collimator and scope adjustment tester some years ago. It was even modified to test scope reticule repeatability from the shock of heavy recoil. Used it to measure several 15 to 30 power scopes including Leupold, Nightforce, Weaver, Nikon and some others. None had adjustments exactly as spec'd. And only the Weaver T20, T16 and T10 held zero from recoil; all others jumped off a bit; some up to 3/4 MOA. And none of the variables held zero zooming throughout their power range.

 

[paphil]

I'm only interested in curing part of the problem in the 9 vs 3 oclock wind difference. By simply canting my scope a small amount and testing it to be about 3/4 moa , I no longer need to have a 3moa hold for one 2 mph wind and a 1 moa hold for wind in the opposite direction. Do it your own way, I have no problem with that. And Top gun, the spin drift does increase faster than the linear equations would suggest but the drop of the bullet is related to the velocity of gravity and since at 2000 yards , I'm at 93 moa, the canted allowance would be about 3.7 X the 1 moa for 1000 yards . a little over 74". If anyone has a program to dope spin drift, I'd be curious to know what it is at 2000 yards!