OzFclass

Hi Alan, why not and in the best of spirit. David.

The 1000 yard challenge at Rosedale on Sunday might be the ideal distance to do a bit of load testing. Lets see how my donut shaped groups go over the footrot flats.

williada wrote:Maybe I could shoot Pennant again, work with you and a small group and see if the team can giver Frazer's mob a tickle up Not that I think you need much help seeing you won scratch and handicap at Lang Lang last week. Cheers, David.

David, that sounds like a great idea.

Fixed a few typos and added a bit more to previous posts. I tend to put thoughts down before I lose them, so things get a bit rushed at times without full explanation and linking. David.

Dave,

Would you say longer bullets take longer to "go to sleep" than shorter bullets?
If so would a .308 with 155gn bullets require different testing distances to a 180gn 7mm bullet or a 80gn .224 cal bullet? Or would this just be at the shorter testing distances?

There is an interesting "Challenge" by Bryan Litz, over on the LRH forum.

i.e. shooting through a close range target to see if its possible that the group actually ends up smaller in its MOA size at a longer distance than it does at a shorter distance.

Worth a read as some people say that their rifle shoots better at long range than it does at short range.
I thought it seem to fit in with this topic a bit maybe?

http://www.longrangehunting.com/forums/f19/applied-ballistics-shoot-thru-target-challenge-144359/

The thread goes for 12 pages but there is some very interesting "shoot through target" field tests undertaken by Bryan that make it worth a read.
Anyone want a free trip to the USA!

Norm - we should have our own similar challenge here.
The obvious answers lie in either parallax OR compensation rather than stabilization of bullets. Physics does not allow for angular accuracy to improve with bullet stabilization - Bryan is just trying to show it in the real world BUT

Parallax and compensation (velocity driven) accuracy issues can improve with range- the challenge should be to prove a tightening of groups at a particular distance. A thru target test of parallax will not improve as it is in aiming errors and those errors will continue on BUT compensatory errors may well improve.

so as an example -using a 100m target. Do some testing similar to Williada's suggestion. - deliberately create some velocity spread (e.g. 80 fps range). To be fully compensated at 1000 yards you would need 2 minutes of vertical drop at 100m over this increase in velocity. To do same at 500 yards would only be in the order of 0.5-0.6 minutes (often observed and quite doable).

So - find a good compensatory load (but with poor velocity spread) - and prove to Bryan that indeed the vertical component does tighten up with increasing distance to a point and then it opens up again..............

This will work particularly well on a thru the target test because the original angular accuracy of each shot will be the same.

Also an interesting article on the subject at http://www.appliedballisticsllc.com/Art ... Swerve.pdf

Dave's right, and I quickly skimmed through Litz's work where he argued his work was not responsible for decrease in group size at long range with regard to the corkscrew trajectory. That is true because the corkscrew path of the trajectory doesn't get any tighter past the funnel exit of your best tune, but he did not account for the gravity effect on compensation which pulls different trajectories together or separates them based on bore time and bore angle. What I might concede is the distance in which fast precession ceases as I am only going by past technologies. But suffice it to say, I understand the term going to sleep to mean the dampening of the fast precession and other influences and yes, past that point groups won't tighten with respect to gyroscopic factors although they can open up. For practical purposes, I can relate to 140 yards and what the effects will be out further. There is no way I would test groups for accuracy loads that I felt were significantly coning up short. Anyway, I post now what my response to Norm was and by gee its hard to proof read your own work in the time frame we put it together.


Norm, got home very late last night. Generally, a longer bullet takes more time to go to sleep because if you think about it, we usually use a faster twist rate to stabilize VLD’s for instance. This combined with air flow on a longer nose means the aerodynamic jump is greater. So frictional forces, and twist rates, with the bullet aligning with the air flow largely determine the diameter and length of the cone before a bullet goes to sleep.

You can generally compare bullets using your computer online or with your own ballistic program by finding out what twist rate is required to get a GS of 1.4. High twist rates increase the high frequency yaw (precession) and it follows, it increases the diameter and length of the initial cone.

Do some homework with regard to the pills you describe and when I see you soon, I will tell you if you are right. But for practical purposes, use 140 yards for all calibres we use.

If you want to know more, read below because as usual it is not as simple as it seems.


You know I have been using a 1-15 in .308 lately and seen it is as devastating at 300 yards with less barrel lift, even with Pommy ammo, but it starts opening up at 600. What is killing it, are two things. Firstly, it is a barrel with a lower GS. Because the slow precession phase is not damped enough its angle of attack does not decrease sufficiently. Its dispersion will open up due to the increasing diameter of its cork screw trajectory in the slow precession phase. Secondly, at the overturning moment when the centre pressure moves a tad and there is insufficient dampening, exposing it to greater aerodynamic instability.

In Gwen’s .308 gear, using a 1-12 and iron sights, she still cleans us scope shooters up and really zings from 600. Her GS factor is higher, so the reverse situation occurs – big cone up short with fast precession and tight corkscrew with slow precession. The twist rate is right for the 155 without over stabilising it, so that tractability is not a factor past that vital overturning section in the trajectory. If she hypothetically used a longer heavier pill, then her GS would be lower resulting in greater dispersion at long range. Her group won't get much tighter due to nodal tuning past 600, or a Optimum charge weight designed to accommodate atmospheric density changes and the slow precession seems fixed, so her level of precision is maintained except for the whims of long range decay. Except to say that mild positive compensation through the force of gravity has decreased her dispersion in elevation.

Her new .223 is also zinging and so I make the point, that all three rifles for practical reasons have been tuned at 140 yards. The coning benefits going past this distance are minimal, like thousandths of inches, but the wind influence really kicks in after this distance.

True, if the wind is constant and the same direction the group analysis is not affected. But the sucker does change and when you least expect it. We know the.223 rifle will not be as good at long range, because the results indicate that, but they are due to its BC decaying faster than her .308. So aerodynamically it is not as good. We know, having experienced the vertical wind shear at Moe, the radial diameter in her .223 is not large enough in torque terms, to buck disturbances compared to your 7mm or her .308. We know if a bullet is moved off a path, it can’t recover and we know on its new path assuming things are held constant, it will still be efficient in GS terms. The .223 is a joy to shoot due to low recoil, but importantly, this means trajectories are not altered due to barrel lift. Scope shooters face a similar dilemma when selecting bag handling calibres to reduce group size. Some things are just a trade off.

It gets a bit complicated comparing bullets in an erratic zone before the bullet goes to sleep. We assume the atmospheric density is constant. The effect of gravity it this section does not change but frictional forces do, initially induced by in-bore yaw and or muzzle blast and then by aerodynamic drag factors, then by gyroscopic stability and then by shifting aerodynamic factors past the overturning moment.

Tangent ogive bullets are probably more prone to in-bore yaw with sloppy armouring and hence the bullet cant as Vaughn emphasizes leads to greater dispersion. They seem to shine in unstable conditions like wind shear and have less aerodynamic jump. But the in-bore yaw can offset the benefits in rough conditions. A longer bullet with a greater bearing surface like a 155 Dyer compared to a 155 Sierra is not subject to as much in bore yaw (quality arguments aside). A VLD with that very long nose can be fussy, but due to its greater length overall, it is subject to aerodynamic jump. But they seem to shine in stable conditions. Unless your smithing is first class, the results on paper can be misleading. It may also be argued that the effect of muzzle blast if not conditioned (Obermeyers bloop tube diameter experiments) can increase dispersion, but the dispersion from muzzle blast was less in smaller calibres from what I have stuck in my head from reading years ago.

I don’t pretend to be a ballistician, but hopefully have a grasp of concepts, nor do I have a program that simulates the results, so I look at the paper to try and work out what’s happening based on established principles that I understand. David.

http://youtu.be/KH9SCbCBHaY

This might help ! David after reading the above post , my head hurts , again . Thank you for ur input !
On another note , I'm finding the 155 hybreds not able to handle light twitchy conditions eg becomes less accurate than the 155.5 full bores . And I seem to be not the only one saying it . I'm hearing that the full bores seem to handle choppy conditions better! Like I said just a theory , not proven !
Has anyone else found this or is it my bad marksmenship? Lol!

Ps David got 60 mm of rain!

Graham, Glad you got a drop, we are getting some too. Great find on You tube. Mate I have been breaking these posts into two parts, you did not have to read on Some say you can't punch sense into people, you only give them a sore head, but you can on a computer. The definition of common sense has changed. There is a difference between what is common and what is good sense. All jokes aside, its horses for courses. I just added to the discussion a bit, for those of us and there are a few who enjoy this stuff. We might not be much good for anything else.

Hybrids?? Was it a marketing exercise? I have not tested them. You know a hybrid can't breed, so they might not be any f...good. Regards, David.

Hybrids?? Was it a marketing exercise? I have not tested them. You know a hybrid can't breed, so they might not be any f...good. Regards, David.

Lol!

Those bloody hybrids may well be a marketing exercise. They have great BC's and it pays to try them but so many people go back to something that is easier to tune. Find a VLD, jam it 10-15 thou and your often cooking with gas!

I shoot 155gr Berger Hybrids and find that elevation wise they are very good and easy to tune.
They also shoot well in the wind but windage is always attributable to the shooter, not the re-loader.
They do say in the marketing of them that you need a 1 in 12 twist which I have. I also jump them 30th.
I found it impossible to tune Palma 155.5's in my chamber/barrel configurations so it is horses for courses.

The fact that the Hybrid cannot breed doesn't worry me at all as once fired they are f....d for anything else.

A mule is a hybrid which cannot breed, being a cross between a Jack donkey and a horse, breed dependent on what you want type of work you want the mule for.

The question is: Is the Berger hybrid a cross between the Palma and the VLD, and, if so, which is the donkey and which is the horse

My personal experience with Hybrids in 308 for 155gr; 185gr and a little 215gr is that they either work or they don't in a given barrel.
If they work then you have the extra BC edge but if they prove difficult to achieve accuracy then just give up and go to the 155.5 or Juggernauts or VLD?
Most of these other pills work in the majority of barrels.
My experience over 6 barrels is that the Hybrids work in about 50% of them.
Don't waste time attempting to get the Hybrids shooting if they don't show promise early.
Cheers
Shane

ShaneG wrote:My personal experience with Hybrids in 308 for 155gr; 185gr and a little 215gr is that they either work or they don't in a given barrel.
If they work then you have the extra BC edge but if they prove difficult to achieve accuracy then just give up and go to the 155.5 or Juggernauts or VLD?
Most of these other pills work in the majority of barrels.
My experience over 6 barrels is that the Hybrids work in about 50% of them.
Don't waste time attempting to get the Hybrids shooting if they don't show promise early.
Cheers
Shane

I have similar experience with all bullets in 7mm Shane. I start with the higher BC offerings and work down till the barrel finds something it likes. Fortunately we have a good selection in 7mm (when they're all available). My guess is that bullet diameter, ogive shape, and weight can all suit one barrel better than another.