A
Augustus
Guest
I recieved the latest version of Noels 375 banded solids today. They ar 6 cals and weigh 369 gr. I will fire them from an 8 twist in a couple of days.
Re: Banded Solids
That should be interesting! How many did you get?
That should be interesting! How many did you get?
Re: Banded Solids
Do you feel the 8 twist will overstabilize the bulets or is Noel telling you it is appropriate.
I am in the process of acquiring 100 of them and intend to shoot them out of a 1:10.5 rate barrel which he felt was suitable. I was under the impression that these 370gr versions were intended for slower twist rates as a compromise. His 400 gr and 421 gr bullets were aparently intended for LGT barrels with a 6.5 final rate and he was looking for a more commonly useable projectile. Had you ever tried either of his heavier bullets in your 8 rate barrel? and if so how did they perform?
I am curious about how much twist rate latitude there is in this equation.
Do you feel the 8 twist will overstabilize the bulets or is Noel telling you it is appropriate.
I am in the process of acquiring 100 of them and intend to shoot them out of a 1:10.5 rate barrel which he felt was suitable. I was under the impression that these 370gr versions were intended for slower twist rates as a compromise. His 400 gr and 421 gr bullets were aparently intended for LGT barrels with a 6.5 final rate and he was looking for a more commonly useable projectile. Had you ever tried either of his heavier bullets in your 8 rate barrel? and if so how did they perform?
I am curious about how much twist rate latitude there is in this equation.
Re: Banded Solids
Mojave,
The 8" twist provides more gyroscopic stability than necessary. At 3,000 fps the Sg is ~1.56, and Augustus will be able to fire the ZA375/6.0-M at much higher velocities than this (which further increases gyroscopic stability).
The whole story is not in the stability factor however.
The over-turning moment wrought havoc on the 6.5, and 7.0, notwithstanding a technically sufficient Sg from the 1: 8.0". Up to 2,800 fps they were fine, but beyond that, dynamic-stability was marginal. A Sg >1.0 is a necessary, but insufficient, condition for dynamic (flight) stability. This is why so much effort was focused on compensating tail geometry for these longer projectiles.
The ZA 6.0 incorporates tail refinements made necessary by the 6.5, and 7.0 experience. For your location (Las Vegas), and time of year, the 1:10.5" twist should be adequate. That would all change if you dropped to sea-level, and lower temperatures. Scott Nye basically demonstrated this at Raton earlier this month when he used a twist-rate two calibers longer than yours, at ~2,600 fps, when testing the ZA50/6.0-M. 90% of the projectiles stabilized, with impressive results. It was simply not possible to drive these 930 grain behemoths any faster with VV 20N29 from the, relatively short, 32" barrel.
Mojave,
The 8" twist provides more gyroscopic stability than necessary. At 3,000 fps the Sg is ~1.56, and Augustus will be able to fire the ZA375/6.0-M at much higher velocities than this (which further increases gyroscopic stability).
The whole story is not in the stability factor however.
The over-turning moment wrought havoc on the 6.5, and 7.0, notwithstanding a technically sufficient Sg from the 1: 8.0". Up to 2,800 fps they were fine, but beyond that, dynamic-stability was marginal. A Sg >1.0 is a necessary, but insufficient, condition for dynamic (flight) stability. This is why so much effort was focused on compensating tail geometry for these longer projectiles.
The ZA 6.0 incorporates tail refinements made necessary by the 6.5, and 7.0 experience. For your location (Las Vegas), and time of year, the 1:10.5" twist should be adequate. That would all change if you dropped to sea-level, and lower temperatures. Scott Nye basically demonstrated this at Raton earlier this month when he used a twist-rate two calibers longer than yours, at ~2,600 fps, when testing the ZA50/6.0-M. 90% of the projectiles stabilized, with impressive results. It was simply not possible to drive these 930 grain behemoths any faster with VV 20N29 from the, relatively short, 32" barrel.
Re: Banded Solids
Almost 370 grainers that is mucho heavy. i think 8 twist would work. Most out there are 333 to 350 if I am not mistaken
Almost 370 grainers that is mucho heavy. i think 8 twist would work. Most out there are 333 to 350 if I am not mistaken
Re: Banded Solids
Noel, this may sound neewb but how are you able to determine the tail instability? How the round hits the target? High speed photogs at the target? Random patterns at specific ranges? Math?<I simplified this question a bunch. Maybe unexplained fliers at certain longer distances?
Noel, this may sound neewb but how are you able to determine the tail instability? How the round hits the target? High speed photogs at the target? Random patterns at specific ranges? Math?<I simplified this question a bunch. Maybe unexplained fliers at certain longer distances?
Re: Banded Solids
Mechanic,
The process was much simpler than you might think.
We were able to determine the effects of tail configuration, upon stability, through the baseline skills of the testers as marksmen, measured against bullet orientation/dispersion as determined on the target.
I had some idea, conceptually, of air-flow effects upon the tail profile, and made revisions accordingly.
Mechanic,
The process was much simpler than you might think.
We were able to determine the effects of tail configuration, upon stability, through the baseline skills of the testers as marksmen, measured against bullet orientation/dispersion as determined on the target.
I had some idea, conceptually, of air-flow effects upon the tail profile, and made revisions accordingly.
Re: Banded Solids
So more trial and error? When you say bullet orientation do you mean looking at the target paper and seeing keyholing?
So more trial and error? When you say bullet orientation do you mean looking at the target paper and seeing keyholing?
Re: Banded Solids
Yes,
It is trial, and error, but the changes have always improved performance... so I suppose simple "trial, and upgrade" is a better description of the methodology.
The bullet "orientation" I am talking about is the print left on paper. That would include keyholing, angle of inclination, randomness of radial angles, pattern size, etc. You would be surprised at how much information can be inferred from a thoughtful assessment of print patterns in comparing one projectile design to another... when tested at the limits of stability.
Yes,
It is trial, and error, but the changes have always improved performance... so I suppose simple "trial, and upgrade" is a better description of the methodology.
The bullet "orientation" I am talking about is the print left on paper. That would include keyholing, angle of inclination, randomness of radial angles, pattern size, etc. You would be surprised at how much information can be inferred from a thoughtful assessment of print patterns in comparing one projectile design to another... when tested at the limits of stability.
Re: Banded Solids
Thanks Noel,
I do not see myself getting much below the 2000 foot elevation here in Vegas. Most of my other shooting opportunities will be at 6000'+ in Wyoming.
The temperature will be another matter. it is entirely reasonable to expect to see temps in the 20's under hunting conditions. At 6500' el. and @ 20F do you feel the 1:10.5 will provide sufficient stabilization?
Ignoring hunting conditions, if the same 6500' el and 50F were the parameters, can I expect good performance from the 6.0 for long range target work?
Thanks Noel,
I do not see myself getting much below the 2000 foot elevation here in Vegas. Most of my other shooting opportunities will be at 6000'+ in Wyoming.
The temperature will be another matter. it is entirely reasonable to expect to see temps in the 20's under hunting conditions. At 6500' el. and @ 20F do you feel the 1:10.5 will provide sufficient stabilization?
Ignoring hunting conditions, if the same 6500' el and 50F were the parameters, can I expect good performance from the 6.0 for long range target work?
Re: Banded Solids
Mojave,
In a hunting application, the bullet must be stable with a comfortable margin to spare. Even at 6,500', you will be border-line at 20oF. Do not shoot at game in those conditions.
You can expect good performance for long range target work at 50oF, and 6,500' elevation.
I suppose I should also elaborate on the "trial, and error" comment. Every dimension in these projectiles is determined for compromised aerodynamic optimization. Unfortunately, a body of rotation which is aerodynamically ideal cannot be spin-stabilized. The first compromise made to the ideal is the engraving footprint, which contributes nothing to the form factor. Next comes tail surfaces, without which, no projectile would fly nose first.
Aerodynamic efficiency is entirely mathematically determined. Aeroballistic efficiency is still an art, and only informed by aero formulas.
Mojave,
In a hunting application, the bullet must be stable with a comfortable margin to spare. Even at 6,500', you will be border-line at 20oF. Do not shoot at game in those conditions.
You can expect good performance for long range target work at 50oF, and 6,500' elevation.
I suppose I should also elaborate on the "trial, and error" comment. Every dimension in these projectiles is determined for compromised aerodynamic optimization. Unfortunately, a body of rotation which is aerodynamically ideal cannot be spin-stabilized. The first compromise made to the ideal is the engraving footprint, which contributes nothing to the form factor. Next comes tail surfaces, without which, no projectile would fly nose first.
Aerodynamic efficiency is entirely mathematically determined. Aeroballistic efficiency is still an art, and only informed by aero formulas.
Re: Banded Solids
A while ago I had seem some short distance training rounds for the .50BMG with very small fin design on the back and had always wondered if they could be modified to help correct stability (turn over) at the longer distances and transonic range. Similar to if I am not mistaken the stability gain in tracer as tail section gets lighter? Hmmm
A while ago I had seem some short distance training rounds for the .50BMG with very small fin design on the back and had always wondered if they could be modified to help correct stability (turn over) at the longer distances and transonic range. Similar to if I am not mistaken the stability gain in tracer as tail section gets lighter? Hmmm
Re: Banded Solids
Mechanic,
It sounds like you are describing something a little different.
The interaction of CG, CP, mass/density distribution, and rotational velocity is fairly complex.
The stabilization achieved by a forward CG, finned-tail projectile is completely dissimilar to a spin-stabilized projectile.
Mechanic,
It sounds like you are describing something a little different.
The interaction of CG, CP, mass/density distribution, and rotational velocity is fairly complex.
The stabilization achieved by a forward CG, finned-tail projectile is completely dissimilar to a spin-stabilized projectile.
Re: Banded Solids
Noel,
Thanks for the information. Is there a fixed twist barrel rate you would see as ideal for the 6.0 projectile?
Would a 1:9 or 1:8 be more appropriate? I am assuming that an LGT barrel finishing in the 1:6.5twist rate would an unnecessarily fast rate. It would seem that, in a solid projectile, the increased rate would not limit velocities due to "stripping" of the rifling in the velocity range we are talking about but would the bullet suffer in flight from "overstabilization, if in fact such a thing exists.
If the answer is no, and making it clear that the discussion does not apply to jacketed projectiles due to material limitations, why would one not just build a gun with the maximum twist for a given velocity expectation and live with excessive spin rate on lighter/shorter projectiles? What is the downside?
Noel,
Thanks for the information. Is there a fixed twist barrel rate you would see as ideal for the 6.0 projectile?
Would a 1:9 or 1:8 be more appropriate? I am assuming that an LGT barrel finishing in the 1:6.5twist rate would an unnecessarily fast rate. It would seem that, in a solid projectile, the increased rate would not limit velocities due to "stripping" of the rifling in the velocity range we are talking about but would the bullet suffer in flight from "overstabilization, if in fact such a thing exists.
If the answer is no, and making it clear that the discussion does not apply to jacketed projectiles due to material limitations, why would one not just build a gun with the maximum twist for a given velocity expectation and live with excessive spin rate on lighter/shorter projectiles? What is the downside?
Re: Banded Solids
I will find and post a pic of them. Unless Triggerfifty beats me to it.
I will find and post a pic of them. Unless Triggerfifty beats me to it.
Re: Banded Solids
Mojave,
A 26 caliber twist is ideal for the 6.0 caliber ZA projectiles. In the case of the .388, that would be a 1: 8.8" exit-twist, producing a Sg of ~1.4 .
The problem with "overstabilization" is mainly theoretical. It will increase spin-drift, but since that is a predictible quantity, it is not really a concern. It is plausable that an excessive Sg could cause a "nose high" condition in the terminal phase of trajectory. In small calibers I do not know how realistic this concern is. Bryan Litz may want to weigh in on the topic.
The greatest downside of excessive spin is the exaggeration of effects from non-uniform material density, and off-axis projectile release. The design of banded solids, from all manufacturers, generally obviates these effects. Copper bar stock is highly uniform in density, and it is in the nature of engraving-bands to self-align relative to the bore axis in the process of side swaging within both constant-twist, and gain-twist, rifling geometries.
There is also the practical mechanical limitation of running out of band material to side-swage in a true velocity compensated rifling twist.
Mojave,
A 26 caliber twist is ideal for the 6.0 caliber ZA projectiles. In the case of the .388, that would be a 1: 8.8" exit-twist, producing a Sg of ~1.4 .
The problem with "overstabilization" is mainly theoretical. It will increase spin-drift, but since that is a predictible quantity, it is not really a concern. It is plausable that an excessive Sg could cause a "nose high" condition in the terminal phase of trajectory. In small calibers I do not know how realistic this concern is. Bryan Litz may want to weigh in on the topic.
The greatest downside of excessive spin is the exaggeration of effects from non-uniform material density, and off-axis projectile release. The design of banded solids, from all manufacturers, generally obviates these effects. Copper bar stock is highly uniform in density, and it is in the nature of engraving-bands to self-align relative to the bore axis in the process of side swaging within both constant-twist, and gain-twist, rifling geometries.
There is also the practical mechanical limitation of running out of band material to side-swage in a true velocity compensated rifling twist.
Re: Banded Solids
Well found it and funny thing is it was in Triggerfifty's book hard target interdiction. The round with the fins instead of a boat tail. It is in the chapter on Gyroscopic and Dynamic Stability dealing with calculations using PRODAS instead of using the Greenhills formula. They are a a limited range training bullets that use a straight fin to increase the decay of spin and force early destabilization and tumble to limit their range. I would not want to reproduce or post a picture out of his book without his permission. I will just say the projectiles are unique looking to be sure.
Well found it and funny thing is it was in Triggerfifty's book hard target interdiction. The round with the fins instead of a boat tail. It is in the chapter on Gyroscopic and Dynamic Stability dealing with calculations using PRODAS instead of using the Greenhills formula. They are a a limited range training bullets that use a straight fin to increase the decay of spin and force early destabilization and tumble to limit their range. I would not want to reproduce or post a picture out of his book without his permission. I will just say the projectiles are unique looking to be sure.
A
Augustus
Guest
Re: Banded Solids
I have 100 of them. I did fire the heavier versions and posted the results in earlier posts. Out of the 8 twist the 6.5 were stable to around 2800 and the 7s somewhat less. I would not use either of the two in the 8 twist. As stated before I have a Bartlien 6.5 gain twist on the way for those. We will just have to wait and see how things go.
I have 100 of them. I did fire the heavier versions and posted the results in earlier posts. Out of the 8 twist the 6.5 were stable to around 2800 and the 7s somewhat less. I would not use either of the two in the 8 twist. As stated before I have a Bartlien 6.5 gain twist on the way for those. We will just have to wait and see how things go.
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