Wind question

[Oldbloke]

I went to the range today to test some reloads

My old Win M70
30.06
125g matching. (Modified, tip filed off. Now 124g)
3100fps (aprox)
100yards
Wind Willy weather tells me. 18 to 25kph 90deg R to L

Obviously the group is spread out left to right.

My question to the more experienced here is.

How much of that might be due to the cross wind.

I know its a bag of snakes but best guess gents.

I'm thinking perhaps the group might have been closer to 18x25mm if it was calm??

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[on_one_wheel]

If nobody beats me to it , I'll run the numbers through my software after dinner..

[Oldbloke]

If nobody beats me to it , I'll run the numbers through my software after dinner..

Good man.
Why didn't I think of that
No laptop ATM so, I will wait patiently.

[on_one_wheel]

The only bits I'm missing are
Twist and Bullet length

Sierra website had most of the info I needed.but surprisingly didn't list the length.

With the number iv plugged (some guess work 1.215" long and 1 in 10) with wind speed of 6 metres / second (average ) I'm getting exactly 1" drift at 100

Without the wind, that would be a pretty tight group.

[Oldbloke]

Barrel length 22"
1/10
Bullets are exactly 25mm (tip filed off)

Thx O0W. Appreciated

Great info.

Its just my old hunting rifle. Was just looking for ball park.

1" was more than I expected.

Looks like I've hit the jack pot regarding load.

[straightshooter]

Out of curiosity I did the calculations using the quoted data. I assumed the mangling of the tips didn't appreciably alter the BC.
Wind drift works out to just on 0.4".
I would be wary using these projectiles in a 30-06 with the usual 10" twist at higher velocities due to the likelihood of core separation.
They would would be happier with a 16" twist which would be optimum.

[on_one_wheel]

Now you've got me second guessing if I've messed something up.

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[Oldbloke]

I had a look at an old cheat sheet. Slightly different data (slower fps)and wind 16kph @100 yards 1.1".
For my purpose close enough for me.

Also, regarding above qn the original intention was to push them to about 2700fps. However this the most accurate load.
They are not butchered.
Weight variation on the tiped bullets is only abt 0.1gr.
The jacket thickness is about same as many game bullets.
Lead hardness is also about same as game bullets.
Length variation is only abt 0.002"

I'm convinced they will be ok upto fallow.

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BTW the ones shown are an early attempt. I have since made a jig and they are close to perfect.

Edit: looking at the load data I've noticed an error. It's closer to 2950fps.
But I think its all academic.

[on_one_wheel]

Every time I tune your numbers up that group looks better and better.

At 25kph 1.6"
At 15kph 1.0"

Perhaps straight shooter was reading MRAD ?

[Oldbloke]

Every time I tune your numbers up that group looks better and better.

At 25kph 1.6"
At 15kph 1.0"

Perhaps straight shooter was reading MRAD ?

Yeh, perhaps he miss read. All those number easy to slip up.

Thanks again OOW

In the end it is academic. Whether they are 3/4" or
1 1/4" . Plenty good enough for hunting out to about 150yards. But tight groups do help confidence.

Certainly better than I can shoot in the field. The old M70 has surprised me.

[straightshooter]

I don't think I mis read.
You state the wind varied from 18 km to 25 km which gives a maximum variation of 7 km. So I used wind = 4.4 mph, BC = 0.34 and MV = 3100fps for the purpose of calculating the maximum variation in wind drift. It is the variation in wind that determines the horizontal group spread whereas the average intensity of wind determines the amount of horizontal drift of the group center from the point of aim.
For the purpose of calculation I used a standard formula and Ingall's tables.
Please remember that all computation is subject to GIGO especially in the smart phone era.
The finished projectiles in the picture look fairly neatly done but I suspect the much enlarged meplat may degrade the BC considerably.
If you have a drill press with a reliable depth stop you could consider using a small center drill to create a 60 degree chamfered hollow point.

[Lazarus]

https://www.rifleshootermag.com/editori ... s%20better.

[Oldbloke]

Yes, BC will be effected.
They are now and the ones fired were better finished.
Yes, I'm giving them a very small counter sink.

At the end of the day, looks like the group could potentially been, say 5 to perhaps 10mm smaller.
That's all I needed to know and happy with the original group anyway.

I'd like to thank both of you for your trouble and input.

[SCJ429]

Every time I tune your numbers up that group looks better and better.

At 25kph 1.6"
At 15kph 1.0"

Perhaps straight shooter was reading MRAD ?

Are you assuming that the wind during some shots was blowing at zero mph and during other shots at 15 mph? There would have been a combination of errors which contributed to the size of the group including aiming errors and bullet runout. What is the best group this barrel has ever shot? Does your wind errors bring it under this number?

[Oldbloke]

Every time I tune your numbers up that group looks better and better.

At 25kph 1.6"
At 15kph 1.0"

Perhaps straight shooter was reading MRAD ?

Are you assuming that the wind during some shots was blowing at zero mph and during other shots at 15 mph? There would have been a combination of errors which contributed to the size of the group including aiming errors and bullet runout. What is the best group this barrel has ever shot? Does your wind errors bring it under this number?

Yep. I didn't take any notice of the wind, just shot a few groups to test reloads. Flags going one minute, pretty calm the next.

Best group? Many years ago IIRC about 20mm. Just remember 150gr bullets. W760 powder.

I rarely shoot groups at a range. Just a couple of shots to confirm zero. It's a hunting rifle, nothing special. Stock STD except I floated the barrel many moons ago.

And the rifle was a safe queen for perhaps 10 years.

[on_one_wheel]

Every time I tune your numbers up that group looks better and better.

At 25kph 1.6"
At 15kph 1.0"

Perhaps straight shooter was reading MRAD ?

Are you assuming that the wind during some shots was blowing at zero mph and during other shots at 15 mph? There would have been a combination of errors which contributed to the size of the group including aiming errors and bullet runout. What is the best group this barrel has ever shot? Does your wind errors bring it under this number?

No I'm calling poltergeist interference on that shot.

Also was the breeze consistent, gusty or intermittent and the same at his range as recorded at a random weather station perhaps 30km from his actual location?
Neither you or I can answer those questions.
The only thing we can do is tell OB that a breeze of 25kph from 90deg will push his projectile off target around 1.6"
Don't worry, I understand what you're saying, not all shots landed 1.6" to the right, yes one shot was even aligned perfectly over centre, did the wind hold its breath for a few seconds while he took that shot ? Shooter error like inconsistent cheek weld or misplaced trigger finger or perh an ichy nose? Earth tremor ? Did a clumsy bird fly into his target frame right before impact or perhaps the target itself flinched?
So many mysteries.

At the end of the day, Old bloke is more than happy with his hunting loads and that's all that really matters.

[SCJ429]

If the rifle normally shoots just under one inch groups and this group is 1.6 inches, then I would conclude that the wind doubles the size of this group. It is only a small sample, four shots, and subsequent groups may have more vertical and less horizontal dispersion while being shot in the same wind conditions. Filing the points off the projectiles isn’t doing the size of the groups any favours.

[Oldbloke]

Yes, happy with what I got.

Wind was 15km away.

To add to the fun, noticed forend screw was very loose last night. Didn't notice it at the range or what I cleaned it tho.

Currently sitting and a fukn fox just run past. He was on a mission. Lol
Didn't respond to the button whistle.

[Oldbloke]

It's all academic. It needs to hit a small plate at 130 yards.

[in2anity]

here's our strength factors for quickly caculating windage:

(NRAA standard flag)

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Going down a factor or two and then back to constant again can (and most frequently does,) happen and is precisely what the shooter monitors for during a stage. Often referred to as the "dropoffs". Similarly, going upward happens during a "gust".

Depending on the exact location and topography of the land, there is a direct correlation between wind direction and stability. For example here on the East coast, a sea breeze is mostly fairly constant. Where a South-Easter is notoriously more inconsistent, and should be monitored with a great deal more care. Such localised knowledge is the "homeground advantage"!

So given that fact, let's say your wind was dropping off from mostly a '4' to a '2' every now and again, without you noticing, that's a momentary 100m difference of 1/2" for even a bleeding edge 155gr palma load driven at 3000fps (.5bc). And I daresay you're not running a 32" barrel with HOT Berger 155gr palma handloads, so your 100m results will likely be worst than 1/2". For example a typical 55gr 223 load will be a 1" horizontal deviation in the aformentioned scenario, i.e. the wind drops to 12km/h for a moment, when it's mostly 25km/h constant.

This would perfectly explain your waterline.

[in2anity]

And this is all presuming the wind direction remained constant, which will often not be the case.

Contrary to what seems intuative, a 90° crosswind (aka "full value") is often the most desirable. For full value, small fluctutations in angle have the least effect on your windage, provided the strength more or less remains the same.

In contrast, it the wind is a head or tail, a minor say 15° change in angle can result in signiifcant angular error on target. In an instant, you can go from a point one side to a point the other (or more, scaling with distance), which can easily go unoticed.

[Oldbloke]

Thankyou in2anity. All very interesting.

Learnt a bit about wind this week.

[on_one_wheel]

It's not that often I need to factor wind when hunting, generally I'm within 150m so an inch or so of drift isn't a big deal.

Occasionally I'll plink at 500m, I like to try and guess wind speed by kicking up dust, throwing leaves, watching mirage through the scope or just go by feel, often the guesswork isn't too bad however most of time I bust out my cheep anemometer when the battery isn't flat just to fine tune my guesswork.

Out of interest I just found this, its some great information to completely forget about once your in the field.

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[Oldbloke]

That looks like the Beaufort scale.

Beaufort_Wind_Chart estimate.pdf

(126.31 KiB) Downloaded 64 times

[on_one_wheel]

That looks like the Beaufort scale.

The attachment Beaufort_Wind_Chart estimate.pdf is no longer available

Good one, the Beaufort Wind Chart is even better

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