Wind at 100yards

[Polchraine]

If I very quickly use a ballistics program I find a 155gn .308 cal travelling at 2800 fps will move .53" in a 10mph wind. More Alarmingly, it will move 2.19" at 200 yards.
As I say, for some people that amount is a lot,

DM

Not too surprising ... and certainly not alarming

Without going into differential equations and calculus and making some basic assumptions which will not be totally true but close enough

Assume:
The wind is perpendicular to the trajectory - that is left to right or right to left.
Wind is constant along the whole range
Bullet leaves barrel at 800 metres per second (2600 fps)and does not decelerate significantly over 200metres. (1900 MPH is 850 metres per second).

The wind will exert on constant force on the bullet - this force is a constant accelerating force.

To travel 200m takes 0.25 second and thus to travel 10m takes 0.125 second

So, whilst travelling down range for 10 metres in 0.125 second the bullet will be accelerated across the range from zero to say 0.02 metres per second. Then in the second 10 metres it will be accelerated by the same again, reaching 0.04 metres per second and son on until the bullet reaches the target when the perpendicular speed would be 0.4 metres per second.

So, in the first 10 metres, starting at 0 and ending at 0.2 metres per second, the bullet will move just 0.000125 metres (0.1mm) across the range but in the next 10 metres the distance will increase to an additional 0.000375 giving a total of 0.0005m. This will continue and when the bullet has travels from 90 to 100m the cross range distance will be and additional 0.002375 and te total distance 0.0125m or 1.25 cm which converts to 0.49"

That continues until the point of impact and when going from 190 to 200m the cross range distance will be 0.004875 m at the total distance 0.05m - 5cm or 1.96" or four times the offset at 100m


Obviously the speed, weight/mass, wind speed, deceleration and a few other factors will have an effect but the offset at 200m will be (just over) 4 times that at 100m. At 400m the distance will be 16 times that at 100m - or in this example 20cm or 7.8"

[TattooedGun]

If I very quickly use a ballistics program I find a 155gn .308 cal travelling at 2800 fps will move .53" in a 10mph wind. More Alarmingly, it will move 2.19" at 200 yards.
As I say, for some people that amount is a lot,

DM

The wind will exert on constant force on the bullet - this force is a constant accelerating force.

That bit right there is the bit that would have thrown me, and upon reading it twice made me comprehend. (although I stilll might not have it)...

so the 10mph wind in the first 10m pushes the bullet 0.000125m
the 10 mph wind over the second 10m has the acceleration of 0.000125m left (wind from right to left) per 10m forward and additionally the initial 0.000125m not forgetting its already moved over 0.000125m already
then the 10mph wind over the third 10m has the acceleration of 0.000125m left per 10m forward and additionally the 0.000250m accelleration already gained which would be 0.000375m plus the additional 0.000375m already travelled..
so at 30m the bullet would have travelled 30m forward and 0.00075m to the left - (I need to look into the gravitational pull mathmatics... not quite there yet...)
40m = 0.0005m + 0.00075 = 0.00125m left
50m = 0.000625 + 0.00125 = 0.001875m left

is my understanding following the right logic?

(constant Acceleration + sideways momentum) + distance travelled = bullet drift? (in a vacuum - with your assumptions)?

[Dangermouse]

Keep in mind that there is more than one school of thought on which wind has the greater effect on the bullet, as well as the belief that the wind at the muzzle has the most effect, some will argue that the wind down range, when the bullet is travelling slower, has more effect.
Those who shoot heavier bullets will argue that their bullets perform better at deflecting wind down range, and in practise this appears to be true.
Currently in F Class, where there is no weight limit implied on the bullet, many are moving to heavier bullets with several using over 200gn.

There are some mavericks who use the 155.5 Berger's and even Laurie Holland who is re writing what can be done with a .223, which throws the cat among the pigeons.

One thing is for sure (and no one is suggesting otherwise) wind is not a constant and few would attempt/expect to take a wind reading at the firing point and using a ballistic calculator, hit a target 100's or 1000's of yards away.

It's a fun game that is for sure,

DM

[TattooedGun]

To travel 200m takes 0.25 second and thus to travel 10m takes 0.125 second

why?
would it not be 0.0125

200/10 = 20

0.25/20 = 0.0125second....

[Polchraine]

Not quite ...

Because the accelerating force continually increases the sideways velocity, then the amount it moves in each 10m is greater than the previous 10m ...

Distance Sideways Distance travelled Total
from Barrel Velocity in 10m block Distance

m m/s m m
0 0 0
10 0.02 0.000125 0.000125
20 0.04 0.000375 0.0005
30 0.06 0.000625 0.001125
40 0.08 0.000875 0.002
50 0.1 0.001125 0.003125
60 0.12 0.001375 0.0045
70 0.14 0.001625 0.006125
80 0.16 0.001875 0.008
90 0.18 0.002125 0.010125
100 0.2 0.002375 0.0125
110 0.22 0.002625 0.015125
120 0.24 0.002875 0.018
130 0.26 0.003125 0.021125
140 0.28 0.003375 0.0245
150 0.3 0.003625 0.028125
160 0.32 0.003875 0.032
170 0.34 0.004125 0.036125
180 0.36 0.004375 0.0405
190 0.38 0.004625 0.045125
200 0.4 0.004875 0.05
210 0.42 0.005125 0.055125
220 0.44 0.005375 0.0605
230 0.46 0.005625 0.066125
240 0.48 0.005875 0.072
250 0.5 0.006125 0.078125
260 0.52 0.006375 0.0845
270 0.54 0.006625 0.091125
280 0.56 0.006875 0.098
290 0.58 0.007125 0.105125
300 0.6 0.007375 0.1125
310 0.62 0.007625 0.120125
320 0.64 0.007875 0.128
330 0.66 0.008125 0.136125
340 0.68 0.008375 0.1445
350 0.7 0.008625 0.153125
360 0.72 0.008875 0.162
370 0.74 0.009125 0.171125
380 0.76 0.009375 0.1805
390 0.78 0.009625 0.190125
400 0.8 0.009875 0.2

[Polchraine]

To travel 200m takes 0.25 second and thus to travel 10m takes 0.125 second

why?
would it not be 0.0125

200/10 = 20

0.25/20 = 0.0125second....

It should be - that is a type, my calcs have it correct!

[TattooedGun]

Code: Select all

Distance 	           Sideways 	        Distance travelled 	  	            Total 
from Barrel              Velocity                   in 10m block                           Distance

m				m/s				m			        	m
0				0				0				
10				0.02				0.000125				0.000125
20				0.04				0.000375				0.0005
30				0.06				0.000625				0.001125
40				0.08				0.000875				0.002
50				0.1				0.001125				0.003125
60				0.12				0.001375				0.0045
70				0.14				0.001625				0.006125
80				0.16				0.001875				0.008
90				0.18				0.002125				0.010125
100				0.2				0.002375				0.0125
110				0.22				0.002625				0.015125
120				0.24				0.002875				0.018
130				0.26				0.003125				0.021125
140				0.28				0.003375				0.0245
150				0.3				0.003625				0.028125
160				0.32				0.003875				0.032
170				0.34				0.004125				0.036125
180				0.36				0.004375				0.0405
190				0.38				0.004625				0.045125
200				0.4				0.004875				0.05
210				0.42				0.005125				0.055125
220				0.44				0.005375				0.0605
230				0.46				0.005625				0.066125
240				0.48				0.005875				0.072
250				0.5				0.006125				0.078125
260				0.52				0.006375				0.0845
270				0.54				0.006625				0.091125
280				0.56				0.006875				0.098
290				0.58				0.007125				0.105125
300				0.6				0.007375				0.1125
310				0.62				0.007625				0.120125
320				0.64				0.007875				0.128
330				0.66				0.008125				0.136125
340				0.68				0.008375				0.1445
350				0.7				0.008625				0.153125
360				0.72				0.008875				0.162
370				0.74				0.009125				0.171125
380				0.76				0.009375				0.1805
390				0.78				0.009625				0.190125
400				0.8				0.009875				0.2

If you use the code tags, it shoul be pre formatted and keep in line... this is a test which could make me look foolish..

No worries on the typo... just clarifying - I'mn not great at mathmatics at the best of times

[Polchraine]

Keep in mind that there is more than one school of thought on which wind has the greater effect on the bullet, as well as the belief that the wind at the muzzle has the most effect, some will argue that the wind down range, when the bullet is travelling slower, has more effect.
Those who shoot heavier bullets will argue that their bullets perform better at deflecting wind down range, and in practise this appears to be true.
Currently in F Class, where there is no weight limit implied on the bullet, many are moving to heavier bullets with several using over 200gn.

There are some mavericks who use the 155.5 Berger's and even Laurie Holland who is re writing what can be done with a .223, which throws the cat among the pigeons.

One thing is for sure (and no one is suggesting otherwise) wind is not a constant and few would attempt/expect to take a wind reading at the firing point and using a ballistic calculator, hit a target 100's or 1000's of yards away.

It's a fun game that is for sure,

DM

I did suggest my calcs were a simplified way of doing it. Yes, as the bullet slows the sideways effect will be greater, then there is additional wind resistance and wind changes - plenty of variables that will alter final values by a small amount.

I did only do it to show that at twice the range the sideways offset/drift is 4 times as much.

[Polchraine]

Code: Select all

Distance 	           Sideways 	        Distance travelled 	  	            Total 
from Barrel              Velocity                   in 10m block                           Distance

m				m/s				m			        	m
0				0				0				
10				0.02				0.000125				0.000125
20				0.04				0.000375				0.0005
30				0.06				0.000625				0.001125
40				0.08				0.000875				0.002
50				0.1				0.001125				0.003125
60				0.12				0.001375				0.0045
70				0.14				0.001625				0.006125
80				0.16				0.001875				0.008
90				0.18				0.002125				0.010125
100				0.2				0.002375				0.0125
110				0.22				0.002625				0.015125
120				0.24				0.002875				0.018
130				0.26				0.003125				0.021125
140				0.28				0.003375				0.0245
150				0.3				0.003625				0.028125
160				0.32				0.003875				0.032
170				0.34				0.004125				0.036125
180				0.36				0.004375				0.0405
190				0.38				0.004625				0.045125
200				0.4				0.004875				0.05
210				0.42				0.005125				0.055125
220				0.44				0.005375				0.0605
230				0.46				0.005625				0.066125
240				0.48				0.005875				0.072
250				0.5				0.006125				0.078125
260				0.52				0.006375				0.0845
270				0.54				0.006625				0.091125
280				0.56				0.006875				0.098
290				0.58				0.007125				0.105125
300				0.6				0.007375				0.1125
310				0.62				0.007625				0.120125
320				0.64				0.007875				0.128
330				0.66				0.008125				0.136125
340				0.68				0.008375				0.1445
350				0.7				0.008625				0.153125
360				0.72				0.008875				0.162
370				0.74				0.009125				0.171125
380				0.76				0.009375				0.1805
390				0.78				0.009625				0.190125
400				0.8				0.009875				0.2

If you use the code tags, it shoul be pre formatted and keep in line... this is a test which could make me look foolish..

No worries on the typo... just clarifying - I'mn not great at mathmatics at the best of times

I was just about to edit it ...

If you want the spreadsheet, I can email it through - it is very basic but shows how it is calculated.

[ovenpaa]

The other thing to consider is the projectile will endeavour to turn itself directly into the wind, this does not mean it will turn left when confronted with a wind from 9 O'clock but it does mean the forward most part of the projectile (Notice I have not used the word head) will cant in that direction. This should not significantly impact shooting at 100x but will at 1000x