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Wouldn't a shot north -south in a wind from the west lift the poi ?

 

I was assuming a North shot with a West wind where with a Right hand twist it will push it DOWN. Around 0.035 MOA per 1mph FV wind.

 

If shooting South then you are right the shot will lift by same amount.

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DaveT you guessed correct , we shoot north.

 

Mike

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DaveT you guessed correct , we shoot north.

 

Mike

 

Best range orientation for this Hemisphere!

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I was assuming a North shot with a West wind where with a Right hand twist it will push it DOWN. Around 0.035 MOA per 1mph FV wind.

 

If shooting South then you are right the shot will lift by same amount.

sorry. I didn't read your post properly I missed the right deflection part. :)

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I need a cider after reading that!

Different ciders have different effects on cognitive and motor skill performance.Allegedly,effects are stronger in Devon,whether north or south,east or west.But enjoy,and relax. Maybe 'lateral throwoff' won't be mentioned!I think I'll have some refreshment/anaesthetic too!Cheers!

george

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I was assuming a North shot with a West wind where with a Right hand twist it will push it DOWN. Around 0.035 MOA per 1mph FV wind.

 

If shooting South then you are right the shot will lift by same amount.

Agreed,DaveT-compared to just less than an inch of horizontal,a 10 mph cross wind will induce something like 3/8( .35 is more precise!) vertical deflection ( aerodynamic jump) in a 308 168 grain SMK at 2600.

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Mike, there's no way of working out the constant for this method other than matching the output to empirical data.

 

So...your observation that you're always 4-6" (so, 5") out at 600m on a no wind day is perfect:

 

Look up your TOF at 600m and put it in the formula; then play with the constant until it gives you an answer of 5"; the number you find will be the constant for that bullet from your rifle and you can use it to calculate drift for all other ranges and TOFs for that bullet from that rifle.

 

It's a crazy-accurate approximation when done well; compared to doing the 'full non-empirical maths' based on calculated stability factors, the approximation will be within fractions of an inch of the same answer.

 

Yes drift to the right for clockwise twist barrels (I think only the Russians make them with anti-clockwise twist!).

 

There's no rule of thumb relating to vel; in any calibre if I was to guess at one, a bullet that's being spun faster that 'conventional' for it's length will need a higher number; a bullet that's not been spun fast enough will be lower.

 

I wouldn't think about trying to visualise all the effects in a 'oner'. Drift moves your MPI to the right. Then consider the distribution of impacts about that MPI due to deflection and magnus in the normal 'diagonal' way.

 

Just some perspective:

A 6mm 1/12 twist 80 g sierra @3200 will suffer about .4 inch gyroscopic drift,and .1 inch coreolis.With a 5mph wind,an error in wind speed judgement will cause about an inch of error.)Aerodynamic jump(vertical deflection) with 10 mph about 1/2 inch-haven't done the exact math here for same bullet-and these effects might be cumulative,or partially cancel depending on your orientation on the planet!So,if possible

a)sight in!

B) put on weight!!- at 1000yards,155g palma gyroscopic drift is 12.75 inches,300g 338 is 6.5 inches,420g

408 is 2 inches

c)avoid wind!!!

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Just some perspective:

A 6mm 1/12 twist 80 g sierra @3200 will suffer about .4 inch gyroscopic drift,and .1 inch coreolis.

At what distance for the drift value? And at what distance, latitude and bearing of fire for the coriolis?

 

With a 5mph wind,an error in wind speed judgement will cause about an inch of error.)Aerodynamic jump(vertical deflection) with 10 mph about 1/2 inch-haven't done the exact math here for same bullet-and these effects might be cumulative,or partially cancel depending on your orientation on the planet!So,if possible

a)sight in!

Not sure what point you're making, drift is deterministic, it's always there, it's just like saying that when you click your elevation turret to 're-zeroto a new range; you also need to do a few windage clicks for the zero chage due to the fixed drift at that distance. Not sure if that's what you're saying or not :) It's a no-brainer, it's just that most people don't know what to click for drift and therefore it falls into 'too difficult' (when actually it's only turning a turret a couple of clicks) and is therefore not habituated.

 

B) put on weight!!- at 1000yards,155g palma gyroscopic drift is 12.75 inches,300g 338 is 6.5 inches,420g

408 is 2 inches

You can't make statements like that without including other bullet info such as length and rifling twist rate - for example out of the L115 the 338 RUAG round drifts around 12.5inches at 900m (c1000yds)- ie not '6.5 inches' :) Stability, not weight, is the key. :)

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At what distance for the drift value? And at what distance, latitude and bearing of fire for the coriolis?

 

Not sure what point you're making, drift is deterministic, it's always there, it's just like saying that when you click your elevation turret to 're-zeroto a new range; you also need to do a few windage clicks for the zero chage due to the fixed drift at that distance. Not sure if that's what you're saying or not :) It's a no-brainer, it's just that most people don't know what to click for drift and therefore it falls into 'too difficult' (when actually it's only turning a turret a couple of clicks) and is therefore not habituated.

 

 

You can't make statements like that without including other bullet info such as length and rifling twist rate - for example out of the L115 the 338 RUAG round drifts around 12.5inches at 900m (c1000yds)- ie not '6.5 inches' :) Stability, not weight, is the key. :)

 

Sorry,boss.

Distance is 100 yards,location northern hemisphere,not extreme-I can't think that anyone actually calculates with the precision you request,unless they have a very powerful analytic engine,distance is well outwith 'sporting' range,and the target may fire back.It was just to get effects in perspective-the effects of wind error judgement alone(let alone wind's true effect) is generally greater than effects like SD/cor,real though these are.I think I understand what you think you mean by 'deterministic',(known and measureable causal effect-?)and even 'habituated'(habitual?)- I absolutely agree it's just like gravity effect-my figures were to help reduce the unknown aspect-like .4 and .1 inch at 100 yards. Pedantically-I can play the game too-it's not of course a couple of clicks,always,and clicks have differnt adjustment values-but I take this in the spirit I intended-it's a knowable,doable and not large effect in 'field' shooting(I mean sub 400 yards,before we get silly about the size of fields!)But I am sorry it was not put more clearly.Ditto the 'heavy stuff'-I just took another source without checking it's veracity,just to lightly(sic!) make the point,that the effect does vary with bullet/caliber/calibre/etc.If anyone can deal with bullet drop-and most can- most of the rest is similarly calculable,and can be corrected for-as you/I/everyone says-even this uphill/downhill ''poo'' effect,as it has been described.I wonder what 'poo'- meant,in more exact semantic terms.Any ideas?Correction for it is of course in the deterministic domain,though not yet habitual (partly because not everyone knows about it,but then I'm not too sure about vertical coreolis acceleration either.)

Hope this clears the air,of atmosheric variables.Mea culpa!

george

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You lost me somewhere in there :)

 

0.4 drift at 100 would be massive; think your decimal drifted. Coupled with that; I've just never seen anyone give a coriolis correction that wasn't coupled with the latitude and bearing of fire for which it was calculated - unlike drift it isn't 'fixed' to the system and varies according to changes in both lat and bg.

 

Despite that; I suspect we're violently agreeing: put drift on your windage turret (if you know it) whenever you set a new elevation beyond about 600m. If an individual finds that too much effort they may as well give up on setting the elevation too :rolleyes: or changing their watch from BST just to have to change it back 6 months later :lol: . And for rifles; don't even consider coriolis. :)

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You lost me somewhere in there :)

 

0.4 drift at 100 would be massive; think your decimal drifted. Coupled with that; I've just never seen anyone give a coriolis correction that wasn't coupled with the latitude and bearing of fire for which it was calculated - unlike drift it isn't 'fixed' to the system and varies according to changes in both lat and bg.

 

Despite that; I suspect we're violently agreeing: put drift on your windage turret (if you know it) whenever you set a new elevation beyond about 600m. If an individual finds that too much effort they may as well give up on setting the elevation too :rolleyes: or changing their watch from BST just to have to change it back 6 months later :lol: . And for rifles; don't even consider coriolis.

 

I agree with BD... I have worked out the (spin)drift for my rifles out to 1000 yards (it is not enough to be worth factoring in until circa 400 / 500 yards), worked out FV windage for 5, 10, 15 & 20 MPH winds at each 100 yards increment together with the vertical components that go with that wind and put it all intoa spreadsheet that I take an A4 print of with me to the range..... simples! Except for having to judge for NON-FV wind directions and changes, inate bullet dispersion from slightly off-centre bullet manufacture (don't know how to measure that one!) , up & downhill shooting, my own trembling, temperature changing my MV, air density, updrafts from terrain features etc etc ...... SUCH FUN its amazing we hit anything!

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You lost me somewhere in there :)

 

0.4 drift at 100 would be massive; think your decimal drifted. Coupled with that; I've just never seen anyone give a coriolis correction that wasn't coupled with the latitude and bearing of fire for which it was calculated - unlike drift it isn't 'fixed' to the system and varies according to changes in both lat and bg.

 

Despite that; I suspect we're violently agreeing: put drift on your windage turret (if you know it) whenever you set a new elevation beyond about 600m. If an individual finds that too much effort they may as well give up on setting the elevation too :rolleyes: or changing their watch from BST just to have to change it back 6 months later :lol: . And for rifles; don't even consider coriolis. :)

 

My error-the distance was 300yards,to be fairly representative of field shooting.We can I hope peacefully and closely agree-it's a pretty small effect(one 1/8 click at 300?)The point which we all aim for,was to give some mathematical/actual reassurance of that,and I didn't see much point in specifying 'geographically'-beyond temperate N hemisphere-as most readers won't be international globetrotters at least when varminting,and if so can add all this to the atmospheric variables effect,for which I believe good information is available,and altitude,temperature powder burn rate,ignition changes etc.And calculation brain fade under cold conditions!

george

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I agree with BD... I have worked out the (spin)drift for my rifles out to 1000 yards (it is not enough to be worth factoring in until circa 400 / 500 yards), worked out FV windage for 5, 10, 15 & 20 MPH winds at each 100 yards increment together with the vertical components that go with that wind and put it all intoa spreadsheet that I take an A4 print of with me to the range..... simples! Except for having to judge for NON-FV wind directions and changes, inate bullet dispersion from slightly off-centre bullet manufacture (don't know how to measure that one!) , up & downhill shooting, my own trembling, temperature changing my MV, air density, updrafts from terrain features etc etc ...... SUCH FUN its amazing we hit anything!

 

Thanks DaveT, for reinforcing the point that at sub 400 yards,these effects are very small.And that there are other bigger ones!There is of course some 'latitude of acceptance'-ie the targets-whatever they are-are not 'pin points'.Dispersal charts-worst possible scenarios especially - are interesting too,when all the variables act against you-and your 1/4 moa rifle!

george

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