RIP, your comments on the .408 bullet thread raise questions for me that could use some clarification. Rather than put the discussion in the .408" thread or the .510" thread, a separate thread devoted to the topic should help.

quote:

Another thing I recently learned was that this dynamic instability thing may favor the blunter, less pointy, shorter-nosed bullet performance at higher velocity.
So the lesser BC bullet can go faster and not cause the nutational gyrations that open worm holes in the fabric of space-time with the higher BC bullet.

A slightly lesser BC bullet can go faster at MV with less yaw than the higher BC bullet,
thus may be more effective overall in the usual, shorter ranges of big game hunting,
even if the pointy VLD at lower velocity may win at 1000 yards
Hence the Game Field Domination Bullet (GFDB) pet name for this new bullet.

I've seen the remarks about dynamic instability on the GSC website, but I don't know exactly what that means in the physical world, nor how critical it might be as one approaches the boundaries.

Maybe Gerard could enlighten us a bit here. I've also wondered if this is related to some of the problems that may occur with the long plastic tips in the Raptor series. Those needed a hollow point in the plastic, and I had a bunch of lightweight 338 bullets that my rifle didn't seem to like.

Dynamic instability happens when the bullet starts yawing some distance from the muzzle and it could be a recoverable condition or the bullet in flight may not recover. Best is to ensure that it cannot happen and, to ensure that, GSC gives the maximum launch speed. A margin of safety is built into the calculation.

Dynamic Stability (Sd) can be understood by the user in several different ways.

The most basic way is to observe the maximum launch speed given for a particular bullet and not to worry about the calculation that leads up to the max speed specified.

Sd is tied to the muzzle velocity, shape of the bullet and some other factors but it does not always occur and, when it happens, the bullet is usually pushed into yawing by a set of circumstances that work together to create the situation.

The more involved understanding of Sd is that it takes into account that the center of pressure is at the tip of the bullet at the speed of sound. If the bullet is launched at a higher speed, the center of pressure moves towards the end of the ogive/start of the shaft. The higher the launch speed, the more the center of pressure moves away from the tip of the bullet. So, as the bullet slows from the launch speed, the long axis of the bullet becomes 'longer'. If the shift of the center of pressure can no longer be tolerated by the shape of a given bullet, or a circumstance occurs that promotes the condition, the bullet becomes dynamically unstable.

The full understanding of Sd takes a number of factors into account and needs a study of several subjects. It is much longer than what we want to do here and is really the domain of the designer/manufacturer or ballistics person who needs to solve such problems.

Bullets that are dynamically unstable can be accurate. Usually dynamic instability manifests as some unexplained phenomenon like the bullet grouping but not going to the expected point of impact or the bullet simply disappearing.

The targets below show how the same bullet shot at the same distance can be dynamically unstable and, given a different set of atmospheric conditions, very accurate. In both instances the targets were at 300m.

quote:

Originally posted by 416Tanzan:
... I've also wondered if this is related to some of the problems that may occur with the long plastic tips in the Raptor series. Those needed a hollow point in the plastic....

I was told that the hollow point in the plastic was for expansion purposes. Without the hollow point the plastic tip was staying on and the Raptor was acting like a solid.

quote:

Originally posted by tanks:

quote:

Originally posted by 416Tanzan:
... I've also wondered if this is related to some of the problems that may occur with the long plastic tips in the Raptor series. Those needed a hollow point in the plastic....

I was told that the hollow point in the plastic was for expansion purposes. Without the hollow point the plastic tip was staying on and the Raptor was acting like a solid.

The HP within the tip facilitates its obliterating upon impact which assists in initiating expansion of the bullet. The original non-HP tips had a tendency to break at the tip shank resulting in either impeding or prohibiting expansion of the bullet.

The flat base Raptors haven't shown any instability tendencies with either the original long tip or the newer shorter tips. The ESP Raptors with their double ended BBW#13 nose profile did however show extreme tendencies for unstable flight with the tip installed as the resulting bullet balance was to far to the rear of the bullet; as Gerard noted, it would begin oscillating in flight resulting in both poor grouping and key holing at the target.

quote:

Originally posted by Gerard:
Sd happens when the bullet starts yawing some distance from the muzzle and it could be a recoverable condition or the bullet in flight may not recover. Best is to ensure that it cannot happen and, to ensure that, GSC gives the maximum launch speed. A margin of safety is built into the calculation.

...

The full understanding of Sd takes a number of factors into account and needs a study of several subjects. It is much longer than what we want to do here and is really the domain of the designer/manufacturer or ballistics person who needs to solve such problems.

Bullets that are dynamically unstable can be accurate. Usually dynamic instability manifests as some unexplained phenomenon like the bullet grouping but not going to the expected point of impact or the bullet simply disappearing.

See! I told you that nutational gyrations can open wormholes in the fabric of space-time! Bullets VANISH!

The targets below show how the same bullet shot at the same distance can be dynamically unstable and, given a different set of atmospheric conditions, very accurate. In both instances the targets were at 300m.

So the changing atmospheric conditions overcame the margin of safety on that launch speed,
from one group to the next,
or did the handloader surpass the recommended velocity?

I wonder what the velocity of that load was, compared to its recommended max MV? Thanks in advance.

And thanks right now to Gerard for not giving me a headache with all the external ballistics calculus, KISS works fine for me here.

The bullet above is around 80gr (experimental) and the rifle was a 25-06 with a 28" barrel 1:10" twist rate. The calc said that the bullet is good to around 3500fps but it was loaded to 3800fps. The difference between the two groups was that one group was shot with the wind from the left and the other was shot with the wind from the right. This was done at a location where the shooter could stay put and shoot in any direction out to 500m.

The final design bullet that we use for this application is 90gr and good to launch up to 3800fps.

Thank you for these demonstrations. It adds a new dimension for me.

In the past I assumed that adequate twist for lower velocities meant that stability was insured because as a bullet slows down the rotational twist stays about the same so that the number of rotations out to a particular distance increases. The bullet takes a little longer to get there so more rotations take place.

However, it now appears that yaw is more difficult to overcome at higher velocities. So my question then concerns twist and higher velocity limits. I assume that tighter twists would "push the envelope" and allow higher maximum velocity limits. Yes? For example, in the .257" bullet at 3800fps, if the twist were increased from 10" to 8", would the maximum limit be raised above 3800fps?

Something closer to home, I wonder what the maximum velocity would be for a .416" 330gn HV in a relatively slow but standard 16.5" twist barrel?

I finally got a box of these a few months ago and look forward to testing them out the next time I'm back in the US. These bullets will be shot in a 416Rigby CZ550. As a handloader I consider 60000psi-62000psi to be safe in the CZs which produces velocities and energies vonsiderably above SAAMI-limited averages, Pressures like that allow muzzle energies to go over 6000ftlbs, Keeping things just under Weatherby levels seems a practical ceiling. so I tend to cap my loads around 6200ftlbs, assuming good accuracy. I may let up a bit on this for the 330gn HV if it turns out that I can keep the HV shooting at about the same point of impact (100yards) as the TTSX350gn by keeping their velocities similar, around 2800-2840fps. We still have a lot of TTSX ammo in Africa so I will try to tailor the HV loads in the US rifle to match impacts with the TTSX and hope that it works out reasonably close for the African based CZ550 416Rigby.

One must separate the three main components of stability into gyroscopic stability, dynamic stability and tractability. These three factors are separate issues and, although they are related, they have at their origins different factors that control what happens.

No amount of fiddling with the twist rate will have much effect on dynamic stability. The launch speed can be as fast or as slow as one wants, it will not have a great effect on gyroscopic stability and so on. For example,tightening the twist from 10" to 8" on the 257 bullet will increase the gyroscopic stability, have no effect on the dynamic stability and will make the tractability worse.

Being an SP target/tactical bullet, the longer range performance will be compromised. Tractability will decrease, roll out in the direction of the twist of the barrel will increase, and BC over the entire trajectory will worsen, although it may be slightly better initially.

If it were an HV hunting bullet, the closer range terminal performance will increase and the long range terminal performance will decrease.

Asking this question, goes to different issues:

quote:

Something closer to home, I wonder what the maximum velocity would be for a .416" 330gn HV in a relatively slow but standard 16.5" twist barrel?

Maximum launch speed governs dynamic stability and twist rate governs gyroscopic stability. Both will affect terminal performance but at varying distances and, for practical purposes, they are unrelated.

The information to make a good choice is at the Technical Data section on our website and the 416330HV is still on the old format. The new format is far more user friendly. On the old format, and some of these will be around for a while still, the maximum launch speed is often not included but the design will tolerate launching as high as 3900fps.

Dynamic stability in the real world simply means that your bullet has the ability to counter a aerodynamic disturbance over distance in flight.

A obligatory consequence of the act of spinning a symmetrical projectile is precession and nutation.

So claiming that spin rate does not effect dynamic stability is not true, in fact static stability has a direct connection to dynamic instability so has tractability.

Dynamic stability is inversely proportional to static stability Tractability is also inversely proportional to static stability and directly proportional to dynamic stability

In a spatial 3 axis coordinate frame we see that the projectile axis assumes instant attitude position that is not coincidental with the tangent of the arc described by the direction of motion of our bullet.

In aircraft flight this position is described as angle of attack ie nose up or nose down.

In some ballistics circles however this angle is actually described as the angle of incidence ( german = anstellwinkel)

Commonly we see word Yaw angle used ( this is not strictly correct as yaw is the deviation of the long axis in the horizontal plane whilst Lift is used to describe the angle in the vertical plane but as this all occurs whilst the projectile is spinning we simply lump it as yaw

If these two motions are damped out over distance the projectile is deemed dynamically stable. ie the bullet "goes to sleep". or simply put the yaw angle gets smaller over distance.

If the yaw angle grows the bullet is dynamically unstable.

Over longer distance however the bullet now becomes relatively unstable again because the forces acting on the spun bullet causes the attitude of the bullet to change.

Something to consider however.

Euler's gyroscopic equations assume certain mathematical conditions and the most important precondition is that the axis of the spinning body coincides with the tangent of the arc described by the trajectory of the projectile.

This in real life is not true because the launch condition of the bullet at bore egress is random and large angles of yaw are possible. High speed photography and measuring of yaw at bore egress shows that there is a intershot randomness.

The distance at which point the bullet gets to sleep therefore also is random.

Does not dynamic stability equal no yaw, i.e., a quiet, "nose up" (and sub- or super-sonic) bullet, all the way to the target?

Michael, you've just stated things in the way that I've been thinking about them. In particular, if a bullet takes off with a little bit of 'up' attitude relative to the hozizontal access due to barrel elevation over the line of sight in the scope, then if its spin is particularly fast, i.e., with a high stability factor, its 'up' attitude will stay in position and become relatively greater and greater to the trajectory line as the bullet starts to drop due to gravity. Thus an 'overstablilized' bullet might have greater and greater wind resistence, a lowering BC and perhaps loss of stability "way out there".

However, the idea that a maximum velocity stability factor comes into play is new to me and doestn't exactly make sense except to say that at higher muzzle velocities the pressures on the yaw of a bullet cannot be overome, that is, the bullet does not go to sleep. Why an increased spin, an increased twist, would not help in such a situation is not clear to me, but then again, I haven't seen and worked through any equations for maximum velocity instability. .

There is no spin stabilized bullet that has no yaw all the way to the target.

Yaw changes over distance / this is a obligatory consequence of the act of spinning the bullet. There is a sweet window where the bullet has the least yaw, where it has gone to sleep but the further downrange it goes the bigger the yaw grows. So by definition the bullet gets more and more dynamically unstable.

Just as the bullet becomes more statically stable ie the stability factor goes up downrange the dynamic stability factor goes down as does the tractability number.

Over stabilization is not a factor in flat fire trajectories but if you are firing a howitzer canon with a high departure angle it may become an issue.

As to the "up attitude" of the bullet??? does not happen, this is not an aircraft.

The bullet is a spinning body so the "up attitude" is a full circle rotation around it's axis which sits at a angle to the tangent of the arc described by its direction of motion ie precession , superimposed on this are smaller circles ( nutation)

As to " maximum velocity stability" I do not know what this is as linear velocity is not at issue in projectile stability other than at transonic transition.

quote:

Dynamic stability in the real world simply means that your bullet has the ability to counter a aerodynamic disturbance over distance in flight.

1. Such as going subsonic at distance.

quote:

A obligatory consequence of the act of spinning a symmetrical projectile is precession and nutation.

2. This is called gyroscopic stability (Sg) and is determined by the twist/length of bullet and to a much lesser extent, speed.

quote:

So claiming that spin rate does not effect dynamic stability is not true, in fact static stability has a direct connection to dynamic instability so has tractability.

3. Example: A bullet is statically stable and remains dynamically stable over it's entire trajectory. Shoot the same bullet over the same trajectory (but not over the same terrain) it now encounters different atmospheric conditions and becomes dynamically unstable. Question: Same twist, same speed, same bullet same trajectory but different atmospheric conditions. How do you figure that static stability is the cause of this destabilising and not the conditions?

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Dynamic stability is inversely proportional to static stability Tractability is also inversely proportional to static stability and directly proportional to dynamic stability

4. So, according to your reasoning, higher static stability leads lower dynamic stability, high static stability results in less tractability and higher tractability leads to higher dynamic stability.

quote:

In a spatial 3 axis coordinate frame we see that the projectile axis assumes instant attitude position that is not coincidental with the tangent of the arc described by the direction of motion of our bullet.

5. So, higher gyroscopic stability leads to less tractability. Question: At what distance will tractability become a problem, say for a typical 30 caliber?

quote:

In aircraft flight this position is described as angle of attack ie nose up or nose down.

6. True for subsonic speeds and an aircraft carrying people does not spin. Fin stabilised projectiles do spin but can they be classed as aircaft?

quote:

In some ballistics circles however this angle is actually described as the angle of incidence ( german = anstellwinkel)

7. These ballistic circles are wrong. Angle of incidence is Einfallswinkel and angle of attack is Anstellwinkel. There cannot be two different meanings assigned to the same term.

quote:

If these two motions are damped out over distance the projectile is deemed dynamically stable. ie the bullet "goes to sleep". or simply put the yaw angle gets smaller over distance.

8. This condition of nutation and precession does not concern us and are connected to static stability (twist, bullet length, speed). Although nutation and precession fit the definition of dynamic stability, those factors concern us when static stability is considered. Dynamic instability, as it affects us is caused by other factors and occurs (or does not occur) far downrange.

quote:

If the yaw angle grows the bullet is dynamically unstable.

9. Correct but - If a bullet becomes statically more stable as it slows down, a greater yaw angle can only be caused by conditions that do not govern static stability (twist, bullet length, speed)

quote:

Over longer distance however the bullet now becomes relatively unstable again because the forces acting on the spun bullet causes the attitude of the bullet to change.

10. This is called tractability and does not involve nutation or precession and only happens if the intial gyroscopic stability is within a certain range.

quote:

Euler's gyroscopic equations assume certain mathematical conditions and the most important precondition is that the axis of the spinning body coincides with the tangent of the arc described by the trajectory of the projectile.

This in real life is not true because the launch condition of the bullet at bore egress is random and large angles of yaw are possible. High speed photography and measuring of yaw at bore egress shows that there is a intershot randomness.

The distance at which point the bullet gets to sleep therefore also is random.

11. This only becomes a factor where the bullet is jacketed or eccentric. Turned bullets or when bullets are concentric, exhibit so little randomness that it becomes irrelevant.

OMG Gerard:

You surely do not wish for me to respond to all of this ?

Alf, I only asked two questions (my response is numbered now) at 3 and 5. The third question is rhetorical. So, if it is easier for you to say: "1. Agreed/Do not agree/Don't know/Explanation" that will be good.

Gerard,

I appreciate this discussion and wish to see it continue.

In the meantime, would you mind giving some advice on a related topic, an application of stability factors to bullet selection.

If you were going to personally choose a bullet between the
GSC HV .375" 265 grain for a 375Ruger at 2600fps in 12" twist (4000ftlbs)
and
GSC HV .375" 300 grain for a 375Ruger at 2450fps in 12" twist (4000ftlbs),
which would you choose for African plains game, where a buffalo might be included?

Both bullets fit into a Ruger Hawkeye 3.4" magazine.
However, the lighter, shorter bullet appears to have approximately a 25% higher stability factor, while the heavier bullet will resist wind drift better.
The heavy bullet will drop an extra inch at 300 yards, but the light bullet would move sideways an extra 2" at 300 yards in a 10mph crosswind.

What are your thoughts for a 4000ftlb package in 375Ruger?

There is no doubt in my mind that I would use the 265gr HV given that choice. I have a 375H&H and, for that case capacity, it is the one of the bullets to use. The other bullet to consider is the 200gr HV. 300 gr HV is for cartridges that can get it up to a similar speed as what the 265gr HV goes in a 375H&H or Ruger.

If you run the 200gr HV at 3000fps, it produces the same energy as the other two but time of flight is much shorter, trajectory is a lot flatter and wind drift at 300 is about an inch per 5mph more. With this combo a number of PHs find it good for cape buff and exellent for plains game. Some have commented that the combination of 375H&H/Ruger and the 200gr HV, shoots over the same trajectory with the same wind drift as a 300 WinMag with a 180gr bullet, but that it arrives with a lot more authority.

quote:

Originally posted by Gerard:
There is no doubt in my mind that I would use the 265gr HV given that choice. I have a 375H&H and, for that case capacity, it is the one of the bullets to use. The other bullet to consider is the 200gr HV. 300 gr HV is for cartridges that can get it up to a similar speed as what the 265gr HV goes in a 375H&H or Ruger.

If you run the 200gr HV at 3000fps, it produces the same energy as the other two but time of flight is much shorter, trajectory is a lot flatter and wind drift at 300 is about an inch per 5mph more. With this combo a number of PHs find it good for cape buff and exellent for plains game. Some have commented that the combination of 375H&H/Ruger and the 200gr HV, shoots over the same trajectory with the same wind drift as a 300 WinMag with a 180gr bullet, but that it arrives with a lot more authority.

Thank you.
Yes, perhaps I need to rethink the 200grain HV at 3000fps. My wife can handle that in her rifle.

It does have the same basic trajectory as the 300WM out to 300-400 yards, though I would expect the 30 cal bullet to save 3 to 4 inches of 10mph drift already at 300yards.

The recoil with the 200 grain .375" will be less than either the 265 or 300 grain.
And the stability will be very high.
The question remaining is expected depth of penetration compared to the 265grain.
when you say "good" for buffalo, you would expect broadside pass throughs?

We know that the bullet and cartridge combination is capable of accuracy and that load development comes easy. Mention is made 8 paragraphs down on that page. Broadside shots on cape buffalo usually exit (also 8 posts down) and about 50 that we know of were shot so far. Not everybody gives us feedback of course but broadside pass throughs on cape buffalo is the norm.

GSC recommends loading HV and FN bullets about 50fps to 100fps under maximum pressure and then reloaders find that they fight way above their weight.

thank you.

5 out of 6 pass throughs with a 200 grain bullet is surely impressive.

I am guessing that the buffalo pass-throughs 'blew their petals' and still produced impressive internal damage from the flat-nose cylinder phenomenon, where a full flat nose produces a wound channel similar to mushroom. This would argue for keeping the muzzle velocity high enough for an impact over 2700fps (100yards at 3000fps muzzle)for buffalo. Am I pretty much on track?

quote:

11. This only becomes a factor where the bullet is jacketed or eccentric. Turned bullets or when bullets are concentric, exhibit so little randomness that it becomes irrelevant.

The concentry of a turned bullet is not perfect. Your bullets when turned have a +/- tolerance. The material however minute will vary in composition and density. Man made tools producing man made products- no such thing as perfect.

416Tanzan,
You are exactly right. Many reloaders have tried the 200gr HV and they have never gone back to the 265gr HV in 375.

Rusty,
You are correct when you say that no bullet is perfect. However, that is what you said. Not perfectly round, not perfectly uniform in density and not exactly the right size, because there is a tolerance within which we accept that the discrepancies exhibit so little randomness that it becomes irrelevant, is what I said. Have a look at the section titled Bullet Design and Q&A.

The concentricity and tolerance of any turned part is determined by the quality and condition of the spindle bearings, ball screws, slides/linear guides and specification of the machine that is used. When a machine is no longer capable of delivering the specified repeatability and tolerances, it is time to replace the part/s that is causing it to be out of specification. There is a difference between the diameter specification and the roundness specification. We measure for ovality and there we hold a tighter tolerance than what we hold on diameter.

It is a simple matter to measure the delivered parts and decide whether the manufacturer is just advertising or whether the manufacturer can indeed consistently deliver parts that are within specification. We welcome comparison, as long as the measuring equipment is good. Example 1: A customer called to say that our 110gr 270 caliber HV bullets weighed anywhere from 109gr to 113gr. I became concerned and immediately checked all our scales with our set of certified weights. I found that all our scales were within + or - 0.1gr. I called the customer back and he said he would bring his scale and show me. Long story short, when he came in with his scale, we showed him that his scale was dirty and would read the same 154gr weight, placed on the pan repeatedly, with a tolerance of + or - 2gr. Example 2: A customer claimed that our .264" 95gr HV varied in diameter by as much as 0.1 mm. When asked how this was measured, it turns out that the measurements were done with a plastic vernier caliper that is about 15 years old.

Thank you, Gerard.

One last question, pertaining to the information on the GSC website.

Extrapolating from the information for the 375H&H and 375 Ruger, I am guessing that H4895 could push a 200gn HV in the 375 Ruger with about 70 grains, or maybe 72 grains?
Is that a good ballpark figure for H4895 and 375Ruger?

I don't own Quickload, but I'll have two chronographs available for load development.

(Probably will use Rem 9.5Mag primers because my Fed215Match supply is low. I want to save my Fed215M's for 100grain powder loads.)

Hello 416Tanzan,

H4895 will be good although it is a little slow and Rem 9.5mag primers will get the job done. Maximum pressure will be around 3050fps in the 18.5" barrel and I would start the load development at 77gr and load up to between 2950fps and 3000fps.

If the chrono is reliable and reads every shot, there is no need to load more than one at each charge. Stick with the section in load data in the 'Procedure' panel, that is the fastest way to using the least components and allows a structured load development.

Enjoy and let us know how you go.

Thank you, again.

Hmm, 77grains.
A little higher of a starting point with H4895.
The Ruger is a 20" barrel, so it may be fairly easy to reach 3000fps, even with fast powders.

Would H322 be better?
I use it for the 500 ARNyati.

H322 is a little faster and the better powder in this application is H4895. With H322 you would start at 72gr and load to around 2900fps to 2950fps. Maximum pressure is going to be at around 3000fps.

With an extra 1.5 inches at 20", you can work on about 70fps more than 18.5".

It looks like H4895 will be the best for the application and maintaining a velocity around 3000-3050.

Should we want to push the limits, what can be done with Rel-17?

Rel-17 might be good to add to the GSC website as it has been getting a following in the US in medium large case volumes with narrow to medium shoulders. It has worked very well for us in 416Rigby (loaded to 6000-6200ftlbs) and 338WM, so 375Ruger ought to be pretty good.

Rel-17 will work with heavier bullets and will be usable in a 24" barrel and the GSC 265gr HV. It is a very good powder in that application. With the 200gr HV it is too slow for the short barrel.

I have to revise the 265gr load data for the 375 Ruger and will have a close look at it.

H4895 is very energetic. IT IS SPECIAL.
Best possible with heavy bullets in the 400 Whelen.
Works great with the exotic and accurate .411/317-grain GSC HV too.

You do not have to load to "Proof Load" levels like this, but it is possible:


H4198 58.0 grains + 317-grain GSC HV >>> MV = 2482 fps

RL-17 72.0 grains + 400-grain Woodleigh RNSN >>> MV = 2289 fps

VARGET 67.0 grains + 400-grain Woodleigh RNSN >>> MV = 2313 fps

H4895 67.0 grains + 400-grain Woodleigh RNSN >>> MV = 2391 fps

Witnessed by Rusty McGee who said: "Physics does not allow it."

Fool Physics once, shame on me, fool Physics twice, shame on me again ...

BTW,
Gina is working on the 408335HV303 Gamefield Domination Bullet.

Dynamic Instability? I expected to open this thread up and be staring at a picture of ISS! :-)