Spin and stability

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max-x

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What is the current democratic consensus on projectile rpm and stability? What are the benefits of SF's higher than 1.4? Lower than 1.4? What are the drawbacks? Have you experienced significant detrimental torque effects from a fast twist tube? Would you overspin for any reasons other than usability when the temperatures dip to -20C?

Do you have a personal hibernation policy when the temps dip to -20C?
 
I can't answer any of your questions except for the personal hibernation question. That one's answer is yes, I do hibernate when it gets that cold.
 
How about overspinning? What if you run a 2.0? Is there a similar BC penalty for overstabilizing? Has anyone seen on-paper (/rock) improvement at extended ranges due to a reduction in epicyclic swerve?
 
BC rises very slightly as SG rises above 1.5, but this is bullet specific and not a general rule.

Unless you are over-spinning your bullet to the point they disintegrate, super-stability really doesn't do anything. For example, to get a 175gr 30cal to SG of 2.0, you need to reach 3100fps. Hitting 3500fps gets you 2.07.

Super-stable bullets will yaw less way down range than nominally stable bullets, giving slightly less drag. But you'd be better off shooting heavier, slower high BC bullets.

Just aim for at least 1.5 and you'll be good to go.
 
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max-x said:
What is the current democratic consensus on projectile rpm and stability? What are the benefits of SF's higher than 1.4? Lower than 1.4? What are the drawbacks? Have you experienced significant detrimental torque effects from a fast twist tube? Would you overspin for any reasons other than usability when the temperatures dip to -20C?

Do you have a personal hibernation policy when the temps dip to -20C?
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You are overthinking the entire thing. Just go shoot your rifle and forget about everything else.
 
You might find that testing the bullet you want to shoot at various twist rates will be very enlightening.

An SG is simply a number... good, bad, high, low. There are a range of assumptions in what that number really means.

As long as it is above 1.0, the bullet is stable.... how "stable" you want it to be is a subject of debate and testing right now in some circles.

The numbers don't always agree with the target...

But the target is always right.

YMMV.

Jerry
 
Jerry, I can't decide if your information is helpful, confusing or even close to easily useable. As much as I'd like to discount the analytical based approach as voodoo, there are folks who do approach the sport from a scientific background, and in turn, that is what drives progress. Closing with YMMV reflects the information given has an element of 'hack' within it- which considering your experience, surprises me. If SG may be good, bad, high, low, and no one actually knows what it means, why does it exist as a descriptor at all? Why did David Tubb change from a 9 twist to an 8 when he shot straight 243? Random chance? Maybe that was all the local supplier had in stock at the time. Maybe the target gave him a reason. Maybe the math, which is based on observation, can subsequently make accurate forecasts and support descisions.

I would enjoy putting together test regiment to take the debate out of circles as to what does what in the barrel and on paper- if you're interested in sponsoring some equiptment for the test you suggest, I'd be happy to work with you to achieve results.
 
Start to shoot.. try various things.. test for yourself and my vague answer will actually be very clear.

Too much of shooting theory is based on a small sample size test extrapolated over large volume of possibilities.

What applies for one circumstance may not apply to ALL circumstances yet, based on the assumption of the math, it "must".

NOTHING stays constant in this game and even the bullet is a moving target.

I compete, I test and do it under very careful examination. What I see some will not believe and that is ok. What I see is also a small sample size.. my data... but if that data helps me, then that is all that matters.

And ultimately, it is the target that will decide what the "truth" is.

Because what I see is counter to current thinking, I don't bother getting into any more detail... Things will sort out as more shots are fired and more data is collected by a wider range of shooters.

I am just putting it out there to not accept theory on blind faith. Test it for yourself...

Jerry
 
To say that Bryan's work is just theory is far from the truth. Bryan has done more to further the understanding of ballistics that anyone else in our time. What he publishes it backed by testing that follows the scientific method. Many PRS shooters have benefited from Bryan's work and are able to put first round hits on target much more consistently using the knowledge and tools he has created.

bcandsg02.jpg


Looking at his data, it's pretty simple to note one thing in particular: Every single data point with an SG below 1.5 experienced a reduction in BC. The data also show a clear trend of decreasing BC as SG continues to drop. If you have data that contradicts it, then POST IT along with your methodology and equipment calibration/verification methods.

I don't put much stock in the information most put out because it isn't backed with good/any data. It's mostly just superficial observations, and if there is data it usually wasn't collected in a scientific manner.
 
This is an agreeable notion- if the theory does not survive in the dirt, its usefulness is severely limited.

The small sample size is a distinct handicap for developing patterns. If one was to consider that the bore has changed dimension from the first to the fifth shot as a result of thermal expansion, and hence the friction values on the bullet-bore interface have reduced, causing 'change', the entire validity of a string may require caution. Discussing this isn't meant to take away from the enjoyment of the activity, to be sure.

I fully accept that real world data is a key to success, hailing from close to the center-of-the-universe, Ontario, I have been resigned to solving math problems instead of actually testing.
 
kombayotch said:
I don't put much stock in the information most put out because it isn't backed with good/any data. It's mostly just superficial observations, and if there is data it usually wasn't collected in a scientific manner.
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This is what I find difficult to deal with as well. It isn't always that the data isn't there- it's that the data isn't readily accessable. My bet is that there are magazine archives from the Stateside competitoin circles dating back four to five decades with the answers to many questions, however without the detail and robustness of Brian Litz's work. I've found that a data-based approach to choices, such as caliber selection, improves personal performance noticably. For example, looking at cartridge performance from a value perspective on a spreadsheet, 308W is second worst value for performance out there, even considering reloading. It is inexpensive while sacrifcing competitiveness totally.

Kombayotch, I've seen some of the test data you've posted elsewhere, and it appears to be very well done- and useful! I think that it is a fine example of how to properly present data on these topics.
 
Thank you, I'm glad you find it useful.

Magazines like Precision Shooting had some good info go through them. Unfortunately, there isn't much in the way of data from matches stateside. It wasn't until around 2000 when matches started to adopt a practical format. Traditionally, matches were on square ranges at known distances. They always had big target boards and shots were marked with markers to show where the shots were going. Since sighter shots were given, many things could be ignored. Weapon systems weren't as accurate and there were no handheld computers to process ballistic models. We have come a long way because of people like Bryan. Unfortunately, we don't appreciate it as much up here because most of our matches haven't been modernized like they have in the US.
 
kombayotch said:
To say that Bryan's work is just theory is far from the truth. Bryan has done more to further the understanding of ballistics that anyone else in our time. What he publishes it backed by testing that follows the scientific method. Many PRS shooters have benefited from Bryan's work and are able to put first round hits on target much more consistently using the knowledge and tools he has created.

bcandsg02.jpg


Looking at his data, it's pretty simple to note one thing in particular: Every single data point with an SG below 1.5 experienced a reduction in BC. The data also show a clear trend of decreasing BC as SG continues to drop. If you have data that contradicts it, then POST IT along with your methodology and equipment calibration/verification methods.

I don't put much stock in the information most put out because it isn't backed with good/any data. It's mostly just superficial observations, and if there is data it usually wasn't collected in a scientific manner.
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Given that I compete at some matches Bryan goes to and have followed his work since the start, I think I have a little bit of an idea of what he is offering.

Did every bullet get tested? Was it tested in every possible environmental condition?

Were other parameters compared that may have changed with a change to the SG value?

Does increasing SG cause collateral issues?

I don't expect there to be an answer as the testing needed would be massive that only NASA or a Govt funded program could even touch.

For those that have his recent book, how many bullets DID he test? Was it more then the 10 bullets above?

And even with the 10 bullets tested, you have a range of 1.1% to a monstrous 23% change under the test parameters. Doesn't that indicate to you that the process may have varying benefits depending on the actual BULLET?

So, this is where I mean that a little data used to answer ALL questions can be dangerous.

The data I want to see would specific to the bullet and bullet LOT that I compete with.... now what would be interesting

I compete with many talented shooters in Canada and abroad. The use of Bryans work is the genesis of alot of advancements in F class sport. BUT as more testing is done with more options under more conditions, some start to see differences.

With the quality of gear used today and the level of shooting, the results of extremely small changes can be examined. And when that covers hundreds of shots over the same time frame, you get to see interesting trends.

I am not saying the info is bad... I am just saying the info is incomplete. But many are running with it as absolute.

The only way to know is for the shooter to test and see if the benefits outweigh any potential problem. Bullets shapes are changing rapidly and with each change, there is a compromise.... some positive, some unexpected.

The move to try and increase a BC number of a given caliber and weight is a wonderful selling feature. But when some of these bullets are put under very intense testing, it doesn't always go as planned.

If anyone feels that a process is doing it for them, fly at it. The concepts today are indeed more advanced then even a decade ago. But to say the work is complete and absolute....

Shoot a bunch more under varied conditions and you will see for yourself.

Jerry
 
He has DATA. And in his data, every single points with an SG below 1.5 is losing BC. If you want the background behind his data, it's all in his books. It's published for all to be able to read and refute.

If you've got DATA that contradicts his DATA, then POST IT! Some data is better than no data. Actual data in any quantity outweighs stories and superficial observations.
 
Trying to reduce BC as much as possible is not the only important thing when trying to put bullets on small targets way out there.

RPM has affects that go beyond reducing drag... and that gets talked about in Bryan's books too. But for now, the market is all about numbers related to drag so there is a push to provide what consumers want....

As I keep saying, focusing on 1 aspect without understanding its influence on ALL parts of flight can lead to less then desireable results. And this changes with different types of bullets and the conditions they are launched.

You can see Bryan's charts above to illustrate that point.

The data is the observations of very well informed shooters over tens of thousands of rds, dozens of barrels and many matches... since the last Worlds.

It is not like there is some secret handshake you need to get the answer... just test and observe and you will see what I am talking about.

Regardless, if the theory you want to use fits the results you are getting, then it is all good.

Jerry
 
Nothing you have said disproves Bryan's findings about BC being reduced with an SG below 1.5. F-Class shooters shooting tens of thousands of rounds at marked targets does nothing to prove or disprove it. None of them are measuring BC in any way during those matches.

He clearly states in the article:

It’s a common assumption that if a shooter is seeing great groups and round holes, that he’s seeing the full potential BC of the bullets. These tests did not support that assumption. It’s quite common to shoot very tight groups and have round bullet holes while your BC is compromised by as much as 10% or more. This is probably the most practical and important take-away from this test.
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Practical shooters wants higher BC for good reason. Reducing BC a little may not matter when you're shooting at a canned 1000y/900m with a big magnum, sighters and marked shots, but it does matter when you're shooting out to a mile with a small 6mm and all of your shots count. Having an accurate BC matters a lot to those who don't have the facility to test out as far as some of these matches are shooting, to true their ballistics calculators. They have to rely on the published numbers being accurate enough to at least get them close enough to correct the miss (and there isn't an 8 foot target board and markers showing that miss). An accurate firing solution will get you more points in PRS than a slightly smaller group. I'm only able to test out to 700 yards, so I have to rely on my BC being accurate when I shoot at further distances. So far it has been, but I've been diligent in making sure that my barrel and load combination are not compromising it. I don't need a compromised BC on top of the variation already there from manufacturing tolerances and having to deal with velocity changes from temperature.
 
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Again, we are not concerned about only 1 parameter. F class see drift in far greater detail then any other LR shooting sport. We are literally watching to 1/2" of change at 1000yds.

Drift is a HUGE deal to us... if accuracy can be maintained.

Pity you can't test past 700yds. That was the big revelation to me in the last years when I started pushing my testing beyond 800m's... the world would be a whole lot easier if 800m was as far as I competed.

There is little point in worrying about this any further. This process is what you believe and what is working for you. That is all that matters.

All I can recommend is keep an eye on your misses on targets beyond 800m... definitely at 1000yds and beyond. If it all made sense, awesome.

If it doesn't, time to look for a solution.

The one very positive thing about square range shooting on marked targets... we get to tabulate a whole whack of data with very precise measurements and even have the time to compare to a whole range of ambient conditions.

We got data....

Jerry
 
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