Wind

[Seamaster]

Thanks for all the replies chaps, very interesting.

Chris

[Nevbag]

Because the pellet does not see air coming from two different directions it sees the combined flow from the wind and the forward speed. Assuming it is a stable pellet it will try to turn to face the combined air flow (that is the definition of a stable pellet) and therefore will have no flow on the side. The pellet is still being affected by the wind throughout the whole of its trajectory but it is the pellet drag which is making it drift to the side (hence the dependence on BC) not any force on the side of the pellet. The pellet drifts to the side because it is not actually pointing in the direction in which it is traveling relative to the ground so the drag force is pointing slightly to the side as well as to the back giving the pellet drift.
If your pellet does not turn to face the combined air flow you have more problems than wind to worry about.

Many thanks for the explanation B/boy, I will try and file it away in my memory box. I find in life that if I understand the how and why of things I am better able to deal with them.

Nev.

[RobF]

Because the pellet does not see air coming from two different directions it sees the combined flow from the wind and the forward speed. Assuming it is a stable pellet it will try to turn to face the combined air flow (that is the definition of a stable pellet) and therefore will have no flow on the side. The pellet is still being affected by the wind throughout the whole of its trajectory but it is the pellet drag which is making it drift to the side (hence the dependence on BC) not any force on the side of the pellet. The pellet drifts to the side because it is not actually pointing in the direction in which it is traveling relative to the ground so the drag force is pointing slightly to the side as well as to the back giving the pellet drift.
If your pellet does not turn to face the combined air flow you have more problems than wind to worry about.

Has that been born out by observation at the target end? Or is it such a minute amount that it's not visible?

[ballisticboy]

Has that been born out by observation at the target end? Or is it such a minute amount that it's not visible?

Not quite sure what you are referring to but the answer is yes, this is the proven way any projectile behaves in a cross wind. It has been proven by use of spark photography, high speed camera tracking of individual projectiles (called flight follower) and is the basis for the calculations in every fire control system for every gun in just about every army in the world. One outcome of wind drift being the result of drag and not side force is that if you have no drag then there is no wind drift. This is exactly what happens with a sustainer motor on a rocket where the thrust equals the drag, there is no wind drift. Even more strange is that if the rocket is accelerating i.e. the thrust is more than the drag, then the rocket will drift upwind until the motor stops when it will start to drift back down wind like everything else.
I think that is what you were asking but if not let me know.

[Jesim1]

Not quite sure what you are referring to but the answer is yes, this is the proven way any projectile behaves in a cross wind. It has been proven by use of spark photography, high speed camera tracking of individual projectiles (called flight follower) and is the basis for the calculations in every fire control system for every gun in just about every army in the world. One outcome of wind drift being the result of drag and not side force is that if you have no drag then there is no wind drift. This is exactly what happens with a sustainer motor on a rocket where the thrust equals the drag, there is no wind drift. Even more strange is that if the rocket is accelerating i.e. the thrust is more than the drag, then the rocket will drift upwind until the motor stops when it will start to drift back down wind like everything else.
I think that is what you were asking but if not let me know.

All very well and good - technically speaking, but an air rifle pellet is decelerating from leaving the barrel, and in the real world wind is an actual effect, not a theory, and although I understand your logic, the fact of the matter is - if the wind blows from the right - your pellet will land to the left of your target, and vice versa. The explanation may be more astute than this, I get that, but it's the physical and visible results we can observe in our own situations that are what matter - not rockets or vacumes

If we were so obsessed by physics, we would just hang out on the forum and never actually lift or fire a gun - why would we want to

James (I still think it's got something to do with werewolves)

[Rickenbacker]

All very well and good - technically speaking, but an air rifle pellet is decelerating from leaving the barrel, and in the real world wind is an actual effect, not a theory, and although I understand your logic, the fact of the matter is - if the wind blows from the right - your pellet will land to the left of your target, and vice versa. The explanation may be more astute than this, I get that, but it's the physical and visible results we can observe in our own situations that are what matter - not rockets or vacumes

If we were so obsessed by physics, we would just hang out on the forum and never actually lift or fire a gun - why would we want to

James (I still think it's got something to do with werewolves)

I think the point (and the thread) is about comparative 'wind drift' .177 vs .22 cal.

We've already had practical 'in the field' examples on this thread, of some .177's being better than some .22's, and vice versa.

BB explains to us how and why that happens (and that a spin stabilised projectile doesn't actually get blown by the wind), and I fail to see why that knowledge should cause our effing heads to explode?

http://www.exteriorballistics.com/ebexplained/index.cfm
Section 3.2
And most of section 4.
Worth a read ^^^

[PKFusion]

I do like all the theory and have a few of my own, but it's in the field that counts. I am also sad enough to waste time trying to find the answer to that too.

Two of us, both good enough shots for this experiment, took 3 177 rifles and two 22 rifles into a field and shot simultaneously at adjacent targets 40 yards away in a 5-15 mph wind. We compared rifle against rifle. All rifles were shooting their preferred pellets.

Two general conclusions.

1. It is surprisingly difficult to shoot at the count of three!
2. We found no significant difference between calibers or rifles.

Not conclusive, but that's what we found on that day.

[Gunfun]

Does anyone use Chairgun to calculate wind drift ?

You enter the wind speed and angle and Chairgun seems to calculate exact drift in cm or mildots at various ranges using the BC and/or weight of the pellet.

Can anyone more knowledgeable confirm this accurate to in the field/shooting range conditions ?

[Gunfun]

Just had a quick look at Chairgun, on the windage it seems to make no allowance for POI elevation changes due to rifling direction as per an earlier thread discussion. So maybe not that accurate ?

[Rickenbacker]

Just had a quick look at Chairgun, on the windage it seems to make no allowance for POI elevation changes due to rifling direction as per an earlier thread discussion. So maybe not that accurate ?

Furthermore, chairgun would replicate an open space with constant horizontal wind from muzzle to target, based on the BC of an unfired pellet (unchanged by rifling groves and air-blast re-shaping)...

The true measure of a pellet's BC out of your gun is chrono' at the muzzle, and another chrono' downrange (without wind).

Chairgun is probably better for BC comparison than it is for working out drift in inches at a given range...

Of course, there's little point in using a pellet that gives the best BC, if that pellet doesn't happen to group well in your gun... same as there's little point to using a pellet (or calibre) that looses you more through pronounced trajectory than it gains in reduced windage drift...

It's also (perhaps) interesting that a vertical component to wind causes the same degree of vertical pellet deflection as horizontal wind does to the horizontal. Which is much greater than the more minor elevation effects of horizontal tail or head wind, with or without the (also minor) effects of direction of spin vs cross-wind direction.

Now my head hurts...

Have you tried Brian Samson's excellent 'wind game'? http://www.shooting-the-breeze.com/f...ad.php?t=21800

[TonyL]

Excellent stuff, young Phil.

And, Yep, played Brian's game a few months ago.



Now, admittedly not that scientific, nor conclusive, but many years ago I was shooting with a club member and it was hellishly windy that day. Normally Derek's .22 '80 grouped very tightly. On this particularly rough day, his Wasps were all over the place, whereas my 10.5gr H&N Silhouettes were awesome.

Apparently there's a heavier JSB made pellet with a BC superior to the newer H&N Barracuda. If they suited the shooter's barrel, I could only guess that these would be utterly superb in terms of velocity retention, long range trajectory and cheating the wind.

[tommahalk]

Wouldn't it make sense to say the most efficient pellet is the pellet which is least likely to be moved as Mutch in the wind?

[Patrick 2]

The .22 may be affected less by wind beyond 35yds.Have you done any comparisons beyond that range i.e 35yds even if you don't normally shoot beyond that range.

[Brian.Samson]

Which colour cars are the fastest?

I know that in 'theory' it doesn't make any difference, but I don't like to rely on pure theory alone - what do those so called experts know anyway huh?

So in the interests of science I conducted my own tests. I have a blue car and I have a silver car. The blue car is significantly faster than the silver car in both acceleration AND top speed.

Based on my exhaustive testing, it leads me to the conclusion that blue cars are faster than silver cars.

[RobF]

Not quite sure what you are referring to but the answer is yes, this is the proven way any projectile behaves in a cross wind. It has been proven by use of spark photography, high speed camera tracking of individual projectiles (called flight follower) and is the basis for the calculations in every fire control system for every gun in just about every army in the world. One outcome of wind drift being the result of drag and not side force is that if you have no drag then there is no wind drift. This is exactly what happens with a sustainer motor on a rocket where the thrust equals the drag, there is no wind drift. Even more strange is that if the rocket is accelerating i.e. the thrust is more than the drag, then the rocket will drift upwind until the motor stops when it will start to drift back down wind like everything else.
I think that is what you were asking but if not let me know.

Really interesting.

I guess on a pellet though we're talking small amounts as we dont see them go sideways into paper... so would it be something akin to the angle between say the 600mph forward speed and the 10mph sidewind... ie a 600mph sidewind would see the pellet at a 45 degree angle?