OzFclass

Nice post williada thanks. I was reading some benchrest stuff last night and a story was told where at the Anschutz indoor testing range a group would be fired then someone would open a door briefly then close it again and the changed room pressure caused the next group to move over 3/16". I presume this was at 100 yards. Very interesting.

You got it Gyro.

Thank you very much again williada for your detailed reply! I'm still digesting it.

I use postimg.org for storing images online rather than Photobucket. Only limitation with postimg.org is that it must be an image file. Other than that there's none of the annoying things like you get with Photobucket. If you sent images that you'd like posted I'd be happy to upload them to postimg.org

If I understand you correctly, shorter distances can be used to explore the characteristics of a barrel but longer distances are needed to determine a tune as the variation due to conning will mask the finer vibrations which have an effect at longer distances.

You discussion also raises vertical effects due to wind. In smallbore the vertical effects of wind are well known yet in fullbore I was of the understanding that the vertical effects were sufficiently small to be lost in the noise.

May have mentioned it before (you get that way as you age) but the Belmont smallbore range can be a bugger at certain cold months of the year. It's a fully walled in range without roof.

As the range cools from day to night, you get hot air and cooler air sitting one on top of the other until suddenly you can see the meniscus between the two through your scope, at which time high & low eights are in order as it rocks like a water bed somebody's just got off. You can't shoot until the border passes the target.

williada wrote: By orientation, I mean whether node oscillation was 1:1 vertical/ horizontal or 1:2 ( why a plane takes off into the wind?

The outdoor tune orients the bullet nose to the wind flow and influences angle of attack. The nil wind/no lift analogy of hitting an air pocket does not give the pill anything to chew on.

Hi David ! Boy I get a woody, every time u talk about harmonics and external ballistics !

What you saying about head and tail winds effecting angle of attack causing vertical.

This was the basis of my variable Bc gyroscopic procession theory . That I was arguing was part of the culprit of vertical that is experienced at Belmont especially at 1000 yds with head and tail winds .

Note : this is a Neanderthal writing this that is untrained !
When a bullet is torqued it’s in a high rht nose orientation rh twist barrel ( if that’s correct ?) Therefore , when headwinds push into your face and a bullet is fired at long range and /or when the projectile is getting unfriendly with its relationship to kenitc energy and the rpms on that torqued projectile is dropping and getting into the dead speed zone .
The above effect is at its greatest.
I got of tangent ! So wind in face , bullet fired . The normal orientation of the bullet is push slightly high causing more drag and thus shown as a low 6 or high five ! Add to that the lift that comes of some of the mounds or sink for that matter coming of the mountain or mounds and it could be worse ! Low 5 or high 4 even with a 7 mm. I noticed this big time when I was pushing a 180 vld at 900/1000yd under 2770 fps with a 9 twist barrel . Head and tail winds were a huge problem as there wasn’t enough radial torque to keep that pill immune form extra drag or wind sheir. Got a .284 and problem solved ! Pushed them above 2810-20 fps and the problem literally halved!

I’m digressing again! Ive also seen 2 o’clock to 8 o’clock slope in a right hand wind when I.e. projectile is going nearly too slow and it’s giving its last spluttering of energy and stability at the longs . Or twist rate is inadequate by a fly speck and giving the first signs of dynamic stability problems !
The above I call the dead or dying speed zone !

Transonic stability just seems to be wobbling all over the place like a dying spinning top!

Ok back in topic! So a head wind will push the projectile nose higher causing more drag and slower terminal velocity and in general a low shot .
The opposite can be said with a tail wind . It pushes the nose lower thus lowering drag and increased terminal velocity and a high shot ! Add to that a left wind and a right wind can add or subtract lift with aerodynamic jump.
Magnus effect works opposite to Aerodynamic jump but is overpowered by the later .

I think Dave Mac explained the relationship between Magnus and aerodynamic jump.
“ driving down the road with a small 3 cylinder charade doing a 100 keys in 5 th and jumping on the brakes . And it eventually stops. Do we say , lucky we stopped because of the brakes . Or do you say ,lucky we stoped because we had a gutless engine !??”

That’s it ... I’ve run out of puff!
But that the basic theory behind variable bc gyroscopic vertical procession !

You are killing me Sellsy. . Yep those VLD's can be real twitchy and a step up in velocity can help on the right node. Hope the diagram pops up as I am testing !Peter!'s suggestion of a post site to demonstrate with regard to twist rate how your spin drift might fall on an axis. Posted this before and it will be up for a day.

This is a compartment of the big picture and maybe countered by apparent aiming mark shifts or other factors such as a condition of nil wind/no lift if present. It's important to note the angle of attack will vary in different parts of the trajectory. Its important to note the gyroscopic stability has a couple of influences such as projectile base wobble at the start, stabilization then nose wobble comes into play past the overturning moment with greater effect towards 1000 yards as forward momentum rapidly decreases with an increase in the angle of attack.

With regard to radial torque which is determined by the diameter of the projectile, it means its just harder to knock of its line if this force is greater. It might not group better, but on the day it may score better if the conditions suit.


Thanks for the email Alan, hope this is more visible

johnk wrote:May have mentioned it before (you get that way as you age) but the Belmont smallbore range can be a bugger at certain cold months of the year. It's a fully walled in range without roof.

As the range cools from day to night, you get hot air and cooler air sitting one on top of the other until suddenly you can see the meniscus between the two through your scope, at which time high & low eights are in order as it rocks like a water bed somebody's just got off. You can't shoot until the border passes the target.

I remember those nights

GSells wrote:Hi David ! Boy I get a woody, every time u talk about harmonics and external ballistics !

So many lines to reply to that one with ... probably best not to

And thank you again Williada even if every time you post I have to go off and dig deeper!