Wild Day At Range Shooting Into 35-40 MPH Headwind

[samnev]

Went to the range yesterday, 13 mile one way trip, Wind was 5-10 mph when I left home. When I got to the range the wind had picked up to a steady 35-40 mph head wind the temp was 43 degrees. But my brother and I decided to try shooting any way. I was shooting my 308 AIAW which usually shoots bug holes @ 100 yards. My brother was shooting his 308 Remington SPS Tactical. both of us were shooting 168 SMK's @ 2700 fps. The first shot for both of us was dead center on our 1st 1" diamond we were shooting at the next 4 shoots for both of us were progressively lower. The lowest for me was about 3" with the 4 shots almost a perfect vertical string. The same with my brothers next four shots with some horizontal spreading as well. His vertical dispersion was about 4". Both rifles are capable of shooting under 0.5 moa on a good day and my AIAW has never shot group much over 1" and that was when i first got it. My brothers rifle shoots largest group was about 1.5".
Repeated with a 2nd 5 shot group, same results. Pack up and went home. I expected the groups would open up but nothing like we experienced Anyone out there have an explanation on why the wind had such a huge effect on the 168 SMK's. If I was shooting at 500 yards I could understand it, not at 100 yards. By the way just to make sure when I got home checked the scope rings and base, Everything was tight.

I would really appreciate it if someone with a deeper knowledge of exterior ballistics has an answer as to why the large vertical dispersion took place on both our attempted groups.

Thanks in advance.
Sam

 

[mdmp5]

I would say that if the wind was indeed that strong, it was creating all sorts of upwind and downwind, effectively pushing the path of the bullet up and down. Did you use a kestrel to measure that wind velocity?

 

[jashmore1234]

Was the wind rolling over some trees and down onto the range? How was the wind flags or vegetation moving?

Alternatively, was the wind pushing the shooter ever so slightly forward and backward?

 

[308sniper147]

My guess would be a wind "vortex". If you were shooting at a berm then the wind could be whipping down the face of the berm and pushing the bullet downward. Also another thing to consider is obviously at 100 yards while it is traveling it is still reaching it's "apex" point at 100 yards so the downward wind might have created enough force to push the bullet downward. A headwind of that magnitude would creat some major aerodynamic drag but I don't think alone would be enough to push a bullet that much at 100 yards. I am a physics major and honestly this is my best guess. I hopes this helps in any way.



Andrew

 

[tylerw02]

The wind was affecting the shooter and perhaps even the image in the scope.

 

[roggom]

I am thinking it was a combination of environmental conditions and the winds effect on your NPA. Headwind should be zero value, but 40mph will greatly effect velocity, turbulence, etc.

The high wind conditions should have posed a great opportunity to shoot in adverse conditions. I would have stayed and practiced dot drills or just trying to dial in at various ranges. Sub half groups tell me how good my rifle is, hits in 40 mph wind tells me how good I am.

 

[samnev]

The wind was measured on the anemometer the range has. I don't know what brand it was. But on the way home the weather report on the radio said the wind was just to 35 mph. Yes the wind was coming down a high hill behind the 200 yard line. The plastic strips tied to the targets looked like they were in a spiraling vortex at times but mostly moving back towards the shooting line. The range flags were blowing straight out towards the shooting line sometimes moving on a slight diagonal to the shooting line but always fully unfurled. There is no vegetation except for some mossy like plants from the shooting line out to the 200 yard targets. But the trees behind the hill in the 200 yard were moving very vigorously.

 

[308sniper147]

I am thinking it was a combination of environmental conditions and the winds effect on your NPA. Headwind should be zero value, but 40mph will greatly effect velocity, turbulence, etc.

The high wind conditions should have posed a great opportunity to shoot in adverse conditions. I would have stayed and practiced dot drills or just trying to dial in at various ranges. Sub half groups tell me how good my rifle is, hits in 40 mph wind tells me how good I am.

Agreed, I did forget to mention NPA in my post but I would imagine that would have been greatly affected.
And I also agree that I would've stayed and shot at various ranges, it would have presented a fun challenge and one that you don't encounter very often

Andrew

 

[samnev]

The wind was affecting the shooter and perhaps even the image in the scope.

The trigger pulls I got seem to be the same as I usually get with my NF NXS 8-32X56 scope with very little reticle movement noticed. and I never felt I was moving due to the force of the wind. Cant speak for my brother.

As for staying and shooting at various ranges my range only goes to 200 yards. The reason we left was because the wind made it feel so bitterly cold. Us Arizonians are wuss bunnies and not used to shooting in conditions like yesterday.

 

[JSF]

The wind was affecting the shooter and perhaps even the image in the scope.

This is the correct answer. Being in Oklahoma, I have shot in those conditions more than a few times and it is not easy to stay focused. Especially when dirt and shit is hitting you at 40 mph. At 100 yards the wind is not changing the bullets path.

 

[morganlamprecht]

This is the correct answer. Being in Oklahoma, I have shot in those conditions more than a few times and it is not easy to stay focused. Especially when dirt and shit is hitting you at 40 mph. At 100 yards the wind is not changing the bullets path.

i agree with this...i shoot in south tx near the water front and winds are usually 15-25 mph and i have shot a few times in 30+ winds...really hard to focus and stay on target

 

[samnev]

My guess would be a wind "vortex". If you were shooting at a berm then the wind could be whipping down the face of the berm and pushing the bullet downward. Also another thing to consider is obviously at 100 yards while it is traveling it is still reaching it's "apex" point at 100 yards so the downward wind might have created enough force to push the bullet downward. A headwind of that magnitude would creat some major aerodynamic drag but I don't think alone would be enough to push a bullet that much at 100 yards. I am a physics major and honestly this is my best guess. I hopes this helps in any way.

Andrew

Andrew thanks for the reply, I am a retired Physics teacher, small world. I agree with everything you said I know that a strong headwind along with the bullet rotation will move the bullet downward and to the right but the magnitude of the downward deflection is what has me stumped. Exterior ballistics in the Sierra Manual explains this but should not have as much vertical dispersion as I was getting. As I said in my post the shots I got off as seen thru my NF NXS 8-32X56 scope showed no perceptible movement that would account for the results I was getting. The AIAW was shot from a Sinclair front rest and a rabbit ear rear rest. This really has me puzzled as it affected my brothers 308 Remy Tactical the same way with slightly more vertical dispersion and a bit of horizontal spread as well where mine was almost a perfect vertical string. the first shot was spot on the 2nd was 3" directly below it the other 3 in between the first 2. This form a rifle that has shot 5 shot 100 yard groups < 0.2 moa and consistently shots groups < 0.5 moa. The 2nd group was similar to the first.
Next time out hopefully tomorrow if the wind ides down I ail take my 308 TRG 22 (has the same scope) out as well to see how it shoots compared to the AIAW.

 

[samnev]

Update, went to range yesterday. Wind light and variable, temp 65. AIAW is back to shooting 0.5 moa or less. 0.325 moa was my best group 100 yard 5 shot group. So I guess it was the wind causing all the problems on Monday.