It would still be good to have an explanation. I have not heard of a cross wind with no vertical component causing a bullet to rise before. In mountainous regions you can get an updraft on a downwind slope which would effect it a little, a tail component in a wind would reduce drag and cause an effect, but a pure crosswind causing a bullet to raise is definitely a new one on me. Every day is a learning day.
Bullet drop and wind drift
- Thread starter Steve123
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It would still be good to have an explanation. I have not heard of a cross wind with no vertical component causing a bullet to rise before. In mountainous regions you can get an updraft on a downwind slope which would effect it a little, a tail component in a wind would reduce drag and cause an effect, but a pure crosswind causing a bullet to raise is definitely a new one on me. Every day is a learning day.
nun_hunter
Well-Known Member
But remember you HMR is using factory ammo so the consistency isn't going to be a high as most of the cf cartridges which are hand loaded. Most decent CF factory ammo will be more consistent than rimfire ammo especially the HMR.
Is there any reason that the Magnus effect does not pertain?
I remember reading about a rotating cylinder wing and a brief google gave me Magnus effect and Flettner wing...
Presumably with a wind coming from the other direction relative to bullet spin it would cause the bullet to drop faster?
Alan
p.s. this article discusses the Magnus effect on bullets...
Magnus effect - Wikipedia
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A 17 HMR is doing 2500fps, has the aerodynamics of a brick and it notoriously inconsistent. Your 22-250 is probably running 3800fps, the bullet is more slippery and is probably far more consistent. It's like comparing a Smart car with a Ferrari.
Ohh, now you're talking. A wind from the right would cause more lift and from the left more drop, presuming a clockwise rifling. Very theoretical, but you may have a point. I would think that Azimuth, Coriolis effect, Spin Drift, Barometric pressure, Altitude, Temperature and even Humidity are more relevant to a long range shot.
The biggest effect is temperature on your velocity. Running IMR7828 or R15 I'm seeing just over 2.5 fps per degree centigrade. Do your load development in the summer in 20 degrees and then go shooting in 0 degrees and there is 50 fps difference, a huge change in drop and drift outside 500 meters let alone 1000m. Changing to powders that are not due to be banned in June which suffer much lower temperature sensitivity is much more important if you are LR shooting. Unfortunately my Varget loads are to be banned when my stocks run out and there is nothing about that is as good.
Shooting deer at UK ranges life is pretty simple, but get out beyond 500 meters, especially over 1000 meters and the variables are enormous.
As Dodgy says, it's really important to run your real life tests and not just focus on what the ballistic calculator says, but once you have those actuals plugged into the calculator and your actual powder temperature differentials the calculators can be trusted and are really the only way to determine actual drops and drifts in different environments and conditions.
Was shooting my T3 CTR yesterday at 500yds here in Virginia USA. Using the same type factory ammo and have 0.7mil more drop than at home in Ireland. Either the batch of 168gr Hornady Match BTHP bought here was much slower than at home or weather altitude etc. played a bit of havoc. Without a chrono one seems to be a bit in the dark.
edi
edi
It is called the Magnus effect. There is a good section about it in Brian litz'S book applied ballistics for long range shooting. You are indeed correct that other things have more of a dramatic effect on the bullets flight than the Magnus effect but that doesn't mean that it can be ruled out when shooting out to extreme ranges if you are looking for first round hits. You are also correct that your results from a ballistic calculator need checking in real life, but this is to check that you have input all of the variables correctly and that your scope tracks as it should. If you do everything right and have tested your scopes tracking ect. Then the ballistic calculator WILL give a correct output out to transonic range. A lot of people believe that real life is somehow going to be slightly different to the results the calculator give you, this simple isn't true and is down to very few people having a complete grasp on the more subtle ballistic effects.
I can't wait to take into account azimuth, coriolis effect, spin drift, barometric pressure, altitude, temperature and humidity next time I line up on a rabbit with my .17HMR. Oh, and not forgetting Magnus's effect. Crikey. Rabbit isn't gonna stand a chance. There you go Steve123, plenty to get your head around! There'll be a test in two weeks, so come prepared.
reported BC for the 110g Barnes TTSX is .295 with the TSX being even less. My experience with Barnes is that they drop more than expected at range. I have attributed that to the driving band system causing greater drag than the oversimplified G1 based BC suggests. In short make sure you check your bullet drops yourself and then true the ballistic computer to your actual figures rather than assuming the ballistic computer will be correct! It almost certainly will not be correct!!
sir-slots-alot
Well-Known Member
Back to the original question.
The 17 rem is one of the best cartridges out 350 yrds for small varmints and pests species ... especially when there is little wind to worry about.
Its extremely easy to get the little 25 grn Vmax zipping along at speeds in excess of 4100 fps with no loss of accuracy or signs of pressure. Due to these very high muzzle velocities and the relatively short ranges (350 yrds) , the low BC bullets of the 17 cal isn't a major factor.
I have had about five 17 rem rifles and fired thousands of bullets. One simple rule I learnt (the hard way) -- if its howling windy - leave it in the cabinet. The tiny bullets are more effected and buffeted by winds than the heavier 22's and 6 mm pills. On calmer days the 17 rem shines and will keep up with the 22.250 or 20 cal out to 400 yrds.
I currently have a lovely 17 FB - shooting a 25 grn Vmax at 3815 fps. I have dropped quite a few corvids that thought 400 yrds was safe... they were wrong
Video of my old 17 rem in action
The 17 rem is one of the best cartridges out 350 yrds for small varmints and pests species ... especially when there is little wind to worry about.
Its extremely easy to get the little 25 grn Vmax zipping along at speeds in excess of 4100 fps with no loss of accuracy or signs of pressure. Due to these very high muzzle velocities and the relatively short ranges (350 yrds) , the low BC bullets of the 17 cal isn't a major factor.
I have had about five 17 rem rifles and fired thousands of bullets. One simple rule I learnt (the hard way) -- if its howling windy - leave it in the cabinet. The tiny bullets are more effected and buffeted by winds than the heavier 22's and 6 mm pills. On calmer days the 17 rem shines and will keep up with the 22.250 or 20 cal out to 400 yrds.
I currently have a lovely 17 FB - shooting a 25 grn Vmax at 3815 fps. I have dropped quite a few corvids that thought 400 yrds was safe... they were wrong
Video of my old 17 rem in action
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Obviously not an issue with a rim fire, but for first round hits at extreme range it is essential. It was only mentioned to show that horizontal wind does deflect bullets vertically. No one implied that it was a factor when shooting rabbits at medium range.
Minikeeper, thanks for the reply, very educational. Bryan Litz does not include the Magnus effect in any of his ballistic calculation software. I use Shooter and Applied Ballistics and have not seen a field for it. Can you tell us on say a 7mm 0.320 G7BC 168 grain bullet at 2900 fps exactly what allowance has to be made for the vertical component of a 10 mph wind from 90 degrees at 1000 meters?
No argument Ken, I'm genuinely interested to understand this, as it's a new one on me.
Having done quite a bit of homework this morning, particularly looking at what Bryan Litz has to say on the subject, the Magnus force is an important one in explaining bullet stability. At sub sonic speeds it causes the "10 o'clock left, 4 o'clock right" effect that 22 bench rest shooters observe, but at supersonic speeds is has much less effect. Of everything I have read this morning this reply below on Accurate Shooter from Bryan Litz to a question posed by a forum member is probably the most succinct.
Good questions! I think I can help.
The illustration you posted of the Magnus effect is not relevent for a bullet in a crosswind. The reason is because a bullet will point it's nose into a crosswind, like a weather vane, and the wind doesn't actually blow on the side of the bullet as suggested in the illustration.
There is a vertical component of wind deflection, but it's not caused by the Magnus effect.
When the bullet shifts it's axis of rotation to align with the on-coming air,when it 'weather vanes'), this sets up a series of precession cyles which quickly dampen out. The net effect of this precession is called 'aerodynamic jump'. The effect is upward for a left right wind, and down for a left right wind. This 10 O'clock to 4 O'clock diagonal is very familiar to short range benchrest shooters who shoot rifles with enough precision to see the effect clearly. How much vertical deflection you get is related to the gyroscopic stability of the bullet. The higher the stability factor, the more vertical deflection.
The Magnus effect you asked about is real, and has an effect at long range. The effect is called 'spin drift', and acts to the right for right twist barrels. At very long range, the bullet can fly with a slight nose up orientation, which will cause the situation shown in your illustration. Spin drift can be around 6-10" at 1000 yards depending on bullet stability, time of flight, Magnus moment coefficient,which is highly sensitive to Mach number).
I hope this helps sort it out for you.
You can read more about gyroscopic drift and coreolis drift in my website:
http://bryanlitz.bravehost.com/
Click on 'Gyroscopic and coreolis drift'.
Unfortunately the link no longer works. I think my take is that I don't need to worry about the Magnus effect out to 1000 meters, I have enough on trying to work out corrections for all the other factors.
ChesterP
Well-Known Member
The magnus effect is very real but calculating it is not quite that straightforwards because it is proportional to the diameter of the cylinder, its length and it's rotational velocity (spin rate) and to the value of the wind and to the movement of the bullet about it's centre of gravity or rotational stability. In other words, any programme or model would need to model 6 degrees of freedom but most apps only model for the X, Y and Z planes and do not include bullet movements on the pitch, roll and yaw axis.
"Aerodynamic jump" caused by the magnus force and the bullet gyroscopic motions cannot be accurately calculated for a number of reasons best left to those who wish to read the Litz Advanced Ballistics in depth explanations further, but they can be approximated as follows: (note, this is taken from Brian Litz Applied Ballistics for Long Range Shooting (2nd Edition) P78 & 79)
Y = (SG/100) -(0.0024L) + (0.032) MOA/W
Where Y = value of vertical deflection, SG is the bullet stability factor, L the bullet length (in calibres, so a 1.5 inch bullet in say 6.5mm becomes 5.86 calibres) and W the wind speed in MPH. (ie full value of sidewind)
This is the approximation for every 1mph of sidewind so for a 10mph sidewind you would end up with the solution multiplied by 10.
For wind from the left as viewed from behind the bullet, this value has a deflection component which is RIGHT and DOWNWARDS
For wind from the right, this value has a deflection component which is to the LEFT and UPWARDS
Now onto practical considerations. Why is it that competition and BR shooters usually ignore this motion? Perhaps it's because they get sighter shots and because this effect being separate from actual vertical wind deflections (ie due to vertical winds as opposed to Magnus effect and aerodynamic jump) makes it almost impossible to deduce anything from grouping patterns due to the number of variables involved.
The actual vertical wind deflections caused by undulations and thermal differences between shooter and target are generally not significant at closer ranges, but become more so when over long distances, there is more chance of undulating ground, and the true value of these true vertical components varies, so understanding their impact becomes more guesswork and experience since they cannot realistically be modelled.
For long range hunters who want to maximise the chances of a first round hit at long range, then it arguably is worth considering aerodynamic jump as well as observing air movement along the flightpath of the bullet to be fired and adding whatever compensations are thought needed. No sighting shots here!
It does raise an interesting point and that is irrespective of how many amazing looking first round hits on coke cans and beer cans at 1000yds plus you may see on You Tube, the chances of a first round hit at those distances owes more to pure luck and guesswork as much as worrying about the external forces and aeodynamic jump by calculation. That should now be more obvious, so the conclusions are to my mind at least:
1. For deerstalking to 400m, it is not worth thinking about and is for all practical purposes immaterial;
2. For competition target shooting, due to sighter shots being available, it is also probably not worth considering, although changeable vertical components of true vertical winds may be;
3. For ultra-long range varmint hunting or for those countries where long range hunting of large animals is practiced, aerodynamic jump should be a consideration for first round shots because it is material in maximising chances of a hit. I refrain from saying "humane first round kill" because there are simply too many variables involved and luck has to play an important part. My personal views are that it isn't something I would do myself. I'll leave that argument at that;
4. For long range load development purposes, considering the tendency of groups to open up in an exponentially increasing manner as distance stretches out, combined with vertical deflection of wind and aerodynamic jump, one can see that it does more to detract from making meaningful conclusions from group patterns and sizes once beyond say 600 yards, than it does to try and make sense from them. For LR load development it may be wiser to limit drop and BC verifications to no more than 400 yards. That's just a personal view and as I don't have the expertise to say otherwise, maybe those who do might want to comment further.
Edited for clarification of "Length" in the formula
"Aerodynamic jump" caused by the magnus force and the bullet gyroscopic motions cannot be accurately calculated for a number of reasons best left to those who wish to read the Litz Advanced Ballistics in depth explanations further, but they can be approximated as follows: (note, this is taken from Brian Litz Applied Ballistics for Long Range Shooting (2nd Edition) P78 & 79)
Y = (SG/100) -(0.0024L) + (0.032) MOA/W
Where Y = value of vertical deflection, SG is the bullet stability factor, L the bullet length (in calibres, so a 1.5 inch bullet in say 6.5mm becomes 5.86 calibres) and W the wind speed in MPH. (ie full value of sidewind)
This is the approximation for every 1mph of sidewind so for a 10mph sidewind you would end up with the solution multiplied by 10.
For wind from the left as viewed from behind the bullet, this value has a deflection component which is RIGHT and DOWNWARDS
For wind from the right, this value has a deflection component which is to the LEFT and UPWARDS
Now onto practical considerations. Why is it that competition and BR shooters usually ignore this motion? Perhaps it's because they get sighter shots and because this effect being separate from actual vertical wind deflections (ie due to vertical winds as opposed to Magnus effect and aerodynamic jump) makes it almost impossible to deduce anything from grouping patterns due to the number of variables involved.
The actual vertical wind deflections caused by undulations and thermal differences between shooter and target are generally not significant at closer ranges, but become more so when over long distances, there is more chance of undulating ground, and the true value of these true vertical components varies, so understanding their impact becomes more guesswork and experience since they cannot realistically be modelled.
For long range hunters who want to maximise the chances of a first round hit at long range, then it arguably is worth considering aerodynamic jump as well as observing air movement along the flightpath of the bullet to be fired and adding whatever compensations are thought needed. No sighting shots here!
It does raise an interesting point and that is irrespective of how many amazing looking first round hits on coke cans and beer cans at 1000yds plus you may see on You Tube, the chances of a first round hit at those distances owes more to pure luck and guesswork as much as worrying about the external forces and aeodynamic jump by calculation. That should now be more obvious, so the conclusions are to my mind at least:
1. For deerstalking to 400m, it is not worth thinking about and is for all practical purposes immaterial;
2. For competition target shooting, due to sighter shots being available, it is also probably not worth considering, although changeable vertical components of true vertical winds may be;
3. For ultra-long range varmint hunting or for those countries where long range hunting of large animals is practiced, aerodynamic jump should be a consideration for first round shots because it is material in maximising chances of a hit. I refrain from saying "humane first round kill" because there are simply too many variables involved and luck has to play an important part. My personal views are that it isn't something I would do myself. I'll leave that argument at that;
4. For long range load development purposes, considering the tendency of groups to open up in an exponentially increasing manner as distance stretches out, combined with vertical deflection of wind and aerodynamic jump, one can see that it does more to detract from making meaningful conclusions from group patterns and sizes once beyond say 600 yards, than it does to try and make sense from them. For LR load development it may be wiser to limit drop and BC verifications to no more than 400 yards. That's just a personal view and as I don't have the expertise to say otherwise, maybe those who do might want to comment further.
Edited for clarification of "Length" in the formula
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Thank you ChesterP. Just sat down and worked out what it means at 1000 meters for my 280 and 160 TMK's. The result is 0.15 MOA if I'm running your formula correctly, so around 2", which is significant but in comparison to the other external factors is pretty minor.
Nice to be able to explain and put a value to it though.
Nice to be able to explain and put a value to it though.
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ChesterP
Well-Known Member
Brian is concerned with precision target shooting I think and he does make reference in his book that for target purposes where sighting shots are usually made, then the value of complicating apps for aerodynamic jump are questionable since once you sight in, then further shots only have to consider variations in true vertical and horizontal winds. I sort of follow this but at the same time, since the effect changes with strength of horizontal wind, then presumably any significant change part way through a competition might result in a competitor wishing to make calculations for the difference in POI.
This raises another complication in that the change of POI will be wrt the last shot and NOT to zero wind condition (unless the first shot was the zero wind condition) so you can see how complex it all might get! The simpler way to consider it therefore is between shots, only to consider variation from a zero wind condition to allow a relative POI to be calculated but with so many other variables such as ES, wind deflection etc, the truth is that horizontal wind deflection may cause more alteration to points on the board so the ability to read wind remains the key difference between winning scores and also-ran scores.
When ES figures jump from single to double figures, the end result is that these, combined with inaccuracies in reading the wind might also result in greater points drop, so understandably, striving for consistency in bullet performance and the skill of reading conditions might lend enough experience once on target to maximise scoring potential.
An earlier comment made about aerodynamic jump I think still holds true and that is in the real world where temperature changes and changes due to pure wind deflection etc are concerned, they have more significance, so for all but the person looking to maximise first shot on target at long range, it probably isn't worth considering.
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ChesterP
Well-Known Member
Better late than never to respond!
Yes, you're right of course that you pick the BC which approximates best to the shape/form factor of the bullet being used. In this case though, the Hornady Vmax claims have been found wanting, so even if using their supplied figures it doesn't help as you need to undertake your own drop tests to verify the BC value to use for yourself.
A good book for those interested in the finer details of external ballistics is Complete .50-caliber Sniper Course: Hard-target Interdiction: Amazon.co.uk: Dean Michaelis: 9781581600681: Books . It's a hard read but is a in depth manual for shooting 2000+ m
Following a bit of clarification from ChesterP via PM, who is obviously exceptionally knowledgable on this subject, I thought I had better make it a little clearer for those sad enough to be interested in the subject as I cocked up the calculation first time around.
The formula is easier to read as follows:
(SG/100)-(Lx0.0024)+0.032 = Y MOA/MPH
SG is your bullet stability as calculated by things like JBM's stability calculator
L is you bullet length divided by it's calibre, so for my 7mm 160TMK which measures 1.425" the L value is 5.018
The result, Y, is in MOA per 1MPH wind speed, so simply multiply by wind speed to get the answer.
The 280ai which has a 9 twist and an SG of 1.6 with a 160TMK has an Aerodynamic Jump value of 0.036 MOA/MPH, so in a 10 MPH wind it's 4.1" at 1000 meters, up if the wind is coming from the right, down if it's from the left, presuming its a right twist barrel.
It is odd that Coriolis effect is calculated in the various Ballistic Calculators, which at 1000 meters with the above bullet is 3.6", less than the Jump of 4.1".
Every day is a learning day.
The formula is easier to read as follows:
(SG/100)-(Lx0.0024)+0.032 = Y MOA/MPH
SG is your bullet stability as calculated by things like JBM's stability calculator
L is you bullet length divided by it's calibre, so for my 7mm 160TMK which measures 1.425" the L value is 5.018
The result, Y, is in MOA per 1MPH wind speed, so simply multiply by wind speed to get the answer.
The 280ai which has a 9 twist and an SG of 1.6 with a 160TMK has an Aerodynamic Jump value of 0.036 MOA/MPH, so in a 10 MPH wind it's 4.1" at 1000 meters, up if the wind is coming from the right, down if it's from the left, presuming its a right twist barrel.
It is odd that Coriolis effect is calculated in the various Ballistic Calculators, which at 1000 meters with the above bullet is 3.6", less than the Jump of 4.1".
Every day is a learning day.
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