Which Published Berger BCs Are From Predictions Rather than Measurements?

[lawman29]

This thread reminds me of a game from my youth:

"King of the Hill (also known as King of the Mountain or King of the Castle) is a children's game, the object of which is to stay on top of a large hill or pile (or any other designated area) as the "King of the Hill". Other players attempt to knock the current King off the pile and take their place, thus becoming the new King of the Hill.

The way the "king" can be removed from the hill depends largely on the rules determined by the players before the game starts. Ordinarily pushing is the most common way of removing the king from the hill, but there are significantly rougher variations where punching or kicking is allowed. As such, the game is often banned from schools."

Berger no need to worry; if the cheap shots ever stop coming then you might wonder why...

I shoot Berger's: Long Live The King!

 

[JRS]

I shoot Randy's (BIB'S) bullets. Now, I'm the "king of the hill" ;D

 

[6BRinNZ]

This thread reminds me of a game from my youth:

"King of the Hill (also known as King of the Mountain or King of the Castle) is a children's game, the object of which is to stay on top of a large hill or pile (or any other designated area) as the "King of the Hill". Other players attempt to knock the current King off the pile and take their place, thus becoming the new King of the Hill.

The way the "king" can be removed from the hill depends largely on the rules determined by the players before the game starts. Ordinarily pushing is the most common way of removing the king from the hill, but there are significantly rougher variations where punching or kicking is allowed. As such, the game is often banned from schools."

Berger no need to worry; if the cheap shots ever stop coming then you might wonder why...

I shoot Berger's: Long Live The King!

yep +1...just received a new lot of Bergers...very happy.

 

[Jay Christopherson]

nothing more implacable than an evangelist with a cause. ya'll are wasting your breath...er...fingers. or whatever.

 

[Keith Glasscock]

Since different parties are suggesting we have unfairly singled out Berger and Bryan brought up a paper where we give Nosler a pretty hard time, maybe a quote from that paper is appropriate:

Until you launch a public smear campaign across multiple forums, it's hardly the same thing.

I don't know any shooters who read your 'scholarly papers', and take them seriously.

Tell us again how lubricant isn't slippery: http://www.dtic.mil/dtic/tr/fulltext/u2/a568594.pdf

He doesn't want to discuss that. Apparently, taking pressure readings to prove or disprove his own theory would be too expensive, so he tried to do it mathematically.

As the guy with the most experience measuring BC, does 50 yards sound like a good idea when using independent chronographs to determine BC? How about 200? What kind of errors are likely in that short of a range window? I can see a potential for error.

Someone tell me again who the reviewing peers were and what they do for a living. I'm not good with names.

 

[Michael Courtney]

He doesn't want to discuss that. Apparently, taking pressure readings to prove or disprove his own theory would be too expensive, so he tried to do it mathematically.

You know well I have discussed these papers at some length in their own threads. Time permitting, I am happy to discuss any of our published papers, but prefer not to take this thread down every rabbit trail. Start a new thread, cite the paper you want to discuss, and ask your questions or make your comments. A number of people who earn their living in internal ballistics have read our papers on bullet friction and found them to be solid. Our results on coatings were in agreement with results out of ARL: sometimes the coatings slightly increase friction, sometimes friction is slightly decreased. In cases where we have measured the friction of the same bullets, our results are also in agreement with ARL. The advantage of our method is it is much less expensive.

As the guy with the most experience measuring BC, does 50 yards sound like a good idea when using independent chronographs to determine BC?

How about 200? What kind of errors are likely in that short of a range window? I can see a potential for error.

Low BC bullets lose more velocity over 50 yards than high BC bullets lose over 200. The highest BC bullets lose only 245 fps over 200 yards (BC = 0.743, MV = 2750, standard conditions.) Low BC bullets can lose 280 fps over 50 yards (BC = 0.179, MV = 3200 fps, standard conditions).

The chronographs are calibrated at the site so that their determination of velocity is accurate to within 0.1%, which is a random rather than a systematic error so that uncertainties in the mean values decrease with more data points. We usually shoot 10 bullets each over a range of velocities for each bullet tested, reducing the uncertainties by about a factor of three compared with a single shot. Uncertainties are dominated by shot to shot variations in the bullets themselves or how they leave the rifle.

In time of flight BC measurements, the error in the near chronograph is usually a systematic error. A 0.3% error on the near chronograph (9 fps) yields a BC error of 4%. Firing more shots does little to reduce systematic errors if the near chronograph is systematically off one way or the other, even if only by 4-5 fps.

Also note that the only papers where we rely on 50 yard BC measurements are the papers studying stability and damping of pitch and yaw. When you are using BC to study stability or damping of pitch and yaw, a 50 yard chronograph spacing is more sensitive to the effects you are trying to see. The accuracy of the 50 yard spacing is also double checked with a standard bullet that we have measured the BC of many, many times before. It comes up to within 0.5% of the same number every time.

All of our papers comparing original BC measurements with manufacturer specifications have used spacings more like 100-200 yards. In some of our early measurements, we validated the two chronograph method with the simultaneous use of an acoustic method (different from Bryan's acoustic method).

I have attached a graph of what I would describe as a true "custom drag curve" over a wide range of Mach numbers compared the G7 drag function. The error bars are smaller than the data points in most cases. 10-20 shots were fired at each velocity. (We increased the sample size at lower Mach numbers to improve accuracy.) Some data from Litz (2009) is included. Somehow, the other author inferred BCs from M1.34 to M2.68 from when all the Cds were between ~ M2.24 and M2.51. How does one infer Cds purportedly accurate to 1% over a range of M1.34, when one only has measurements over a range of ~ M0.27 or so?

 

[savagedasher]

Now tell us if .03 grains of powder and going from a 1-8 to a one in 13 figures in.It is just figures. Many of shooter here can select the right twist and load and get the yaw out most bullets. If they do that would your BC figure be wrong.
I think someone here ask for you to bring all your knowledge and show him how good you shoot. Larry

 

[Michael Courtney]

Many of shooter here can select the right twist and load and get the yaw out most bullets. If they do that would your BC figure be wrong.

How do you know what your yaw is? How do you know when you've tweaked things to get it out? Our experience with a given bullet and barrel is that the tip of angle is not sensitive to a particular load. If you're tip off angle is varying between, say 0-4 degrees for a given combination, tweaking the load will not reduce the worst case of 4 degrees. You need to change your bullet or your barrel.

The hypothesis that pitch and yaw might be impacting our BC measurements was first raised in 2009, and Bryan Litz computed that a max tip off angle of 11 degrees would cause the low BCs we measured for certain bullets. The increase in drag is proportional to the square of the peak yaw angle, so that an 11 degree peak yaw angle increases drag 4 times as much as a 5.5 degree peak yaw angle.

We tested this hypothesis in various ways which we reported in a later paper, but the most compelling refutation of the idea was when we used a high speed video camera to measure pitch and yaw angles of bullets in flight. Many, many videos and bullets and the largest angle we ever saw was 4 degrees.

Finally measuring the drag effects of pitch and yaw required using a low BC bullet to begin with, setting up three chronographs (10, 160, and 310 feet), and firing dozens of bullets to get good enough statistics to barely see an effect, and the effect damps out quickly in about 50 yards, even in Colorado's thin atmosphere. The added drag of pitch and yaw effect damped out much more quickly in Louisiana's sea level atmosphere.

Unless you have a rifle and bullet combination that is much worse than we measured, pitch and yaw might cost you a 2% decrease in BC over 100 yards.

I think someone here ask for you to bring all your knowledge and show him how good you shoot. Larry

I checked on that and found the invitation came from New York. No thanks. We lived in New York for a while when my wife was on the West Point faculty, and they were seriously unfriendly toward guns up there. I prefer to avoid states that use the Constitution for toilet paper. Now if someone wants to come to Louisiana, we can probably work something out. But I'll probably have my wife or daughter shoot in my stead.

 

[Bryan Litz Ballistics]

He doesn't want to discuss that. Apparently, taking pressure readings to prove or disprove his own theory would be too expensive, so he tried to do it mathematically.

You know well I have discussed these papers at some length in their own threads. Time permitting, I am happy to discuss any of our published papers, but prefer not to take this thread down every rabbit trail.

Rabbit trail, to Courtney, is a subject that he would rather not be brought to the light of day. This pattern is apparent.

Start a new thread, cite the paper you want to discuss, and ask your questions or make your comments.

because that will garner more attention.

A number of people who earn their living in internal ballistics have read our papers on bullet friction and found them to be solid. Our results on coatings were in agreement with results out of ARL: sometimes the coatings slightly increase friction, sometimes friction is slightly decreased. In cases where we have measured the friction of the same bullets, our results are also in agreement with ARL. The advantage of our method is it is much less expensive.

So wasting a small amount of taxpayer money is better than wasting more taxpayer money?

As the guy with the most experience measuring BC, does 50 yards sound like a good idea when using independent chronographs to determine BC?

How about 200? What kind of errors are likely in that short of a range window? I can see a potential for error.

In my opinion, the only thing you can measure with reasonable certainty in 50-200 yards is varmint bullet BC's. Bullets where BC actually matters, you need more range.

The chronographs are calibrated at the site so that their determination of velocity is accurate to within 0.1%, which is a random rather than a systematic error so that uncertainties in the mean values decrease with more data points. We usually shoot 10 bullets each over a range of velocities for each bullet tested, reducing the uncertainties by about a factor of three compared with a single shot. Uncertainties are dominated by shot to shot variations in the bullets themselves or how they leave the rifle.

Here's a brainwave for you. What if the optical planes of the chronographs aren't parallel (as I've found the CED's)? You calibrate the chronographs in tandem and apply the offset. That offset only applies for the particular window you shot thru. What about when the bullets pass thru different parts of the screens? I've worked with CED's extensively and found their optical planes to be highly non-parallel. None of your publications addresses this source of error. Although it is published in modern literature.

Once again, your academic approach lacks basic common sense.

Also note that the only papers where we rely on 50 yard BC measurements are the papers studying stability and damping of pitch and yaw. When you are using BC to study stability or damping of pitch and yaw, a 50 yard chronograph spacing is more sensitive to the effects you are trying to see.

So if the only means to measure something is inaccurate, then... OK?

The accuracy of the 50 yard spacing is also double checked with a standard bullet that we have measured the BC of many, many times before. It comes up to within 0.5% of the same number every time.

And did this standard bullet pass thru the same portion of the chrono window as the other bullets?

All of our papers comparing original BC measurements with manufacturer specifications have used spacings more like 100-200 yards.

but any "useful" BC is measured over more than 200 yards.

I have attached a graph of what I would describe as a true "custom drag curve" over a wide range of Mach numbers compared the G7 drag function. The error bars are smaller than the data points in most cases. 10-20 shots were fired at each velocity. (We increased the sample size at lower Mach numbers to improve accuracy.) Some data from Litz (2009) is included. Somehow, the other author inferred BCs from M1.34 to M2.68 from when all the Cds were between ~ M2.24 and M2.51. How does one infer Cds purportedly accurate to 1% over a range of M1.34, when one only has measurements over a range of ~ M0.27 or so?

And here's "the rest of the story".

Your low Mach number points were fired from reduced charges in standard twist barrels which does not produce the same RPM or stability condition as a bullet fired at standard MV and slowing at long range. Your data points are not an accurate representation of how a bullet flies at that speed when fired under normal conditions.

Once again; academia vs. real world.

And it's noteworthy that you're using this as an example to discredit my data which was actually fired at long range at standard MV from standard twist barrels.

Michael, you're in over your head.

Let me guess, it's now time to move on to...

Child sacrifice! http://tech.mit.edu/V110/N50/jackso.50o.html

Or maybe this is just another 'rabbit hole'.

 

[Bryan Litz Ballistics]

The hypothesis that pitch and yaw might be impacting our BC measurements was first raised in 2009, and Bryan Litz computed that a max tip off angle of 11 degrees would cause the low BCs we measured for certain bullets.

Yes, you're welcome for that by the way, it formed the basis of you're next several projects of USAF funded research on varmint bullets. Frankly, I was grasping at straws to explain how your BC's measured over 100 yards might be so different from mine which were measured over 600 yards.

In retrospect I should have just said; your uncertainty is just more than you think.

But instead, I modeled a scenario in which 11 degrees of yaw might explain the difference between our measurements, now you're trying to use that against me.

Michael.

Gain access to more than 200 yards worth of range.

Test some bullets that people actually care about BC's.

Then we might be able to compare notes.

Until then, we're not comparing notes as much as you are criticizing data that you're unable to verify.

 

[Matthew Schwartzkopf]

Courtney vs the heathens

Check out http://tech.mit.edu/V110/N50/jackso.50o.html

Good for a laugh and it explains Courtney

 

[Michael Courtney]

Rabbit trail, to Courtney, is a subject that he would rather not be brought to the light of day. This pattern is apparent.

The gentleman who posed the question had previously asserted enough confidence in the experimental method that he said he intended to repeat the experiment himself. His sudden assertion that proper friction measurements were impossible without pressure gauges helped me realize it might not be a short discussion. By the way, ARL didn't use pressure gauges either in their friction studies.

So wasting a small amount of taxpayer money is better than wasting more taxpayer money?

We solved an important problem for under $1000. You are welcome to start a new thread if you want to discuss the details, but you seem to prefer jumping to the assertion that our papers were in error. Publish a reply in the scholarly literature if you can document real scientific problems with the work. All you've done so far is complain about who paid for it.

Courtney: The chronographs are calibrated at the site so that their determination of velocity is accurate to within 0.1%, which is a random rather than a systematic error so that uncertainties in the mean values decrease with more data points. We usually shoot 10 bullets each over a range of velocities for each bullet tested, reducing the uncertainties by about a factor of three compared with a single shot. Uncertainties are dominated by shot to shot variations in the bullets themselves or how they leave the rifle.

Here's a brainwave for you. What if the optical planes of the chronographs aren't parallel (as I've found the CED's)? You calibrate the chronographs in tandem and apply the offset.

We ensure that the optical planes are parallel and then add mechanical rigidity so that the planes remain parallel. This occurs prior to calibration.

That offset only applies for the particular window you shot thru. What about when the bullets pass thru different parts of the screens? I've worked with CED's extensively and found their optical planes to be highly non-parallel. None of your publications addresses this source of error.

As noted above, adding the mechanical rigidity keeps the planes parallel. The window we shoot through at 50 yards is pretty small, about 1". It's not hard to keep varmint bullets in a small window at 50 yards. At larger ranges the window is bigger, and obviously less accurate bullets won't be in a 1" window at 100 and 200 yards. But bullets spread through the window of the far chronograph still provide good readings due to our efforts to keep the planes parallel. These are minutia that we have not mentioned in publications. Perhaps we should have, but editors and peer reviewers have often complained about our method sections being too long with minutia. Method details beyond those in the text have always been immediately clarified for US parties contacting us via email.

Courtney: Also note that the only papers where we rely on 50 yard BC measurements are the papers studying stability and damping of pitch and yaw. When you are using BC to study stability or damping of pitch and yaw, a 50 yard chronograph spacing is more sensitive to the effects you are trying to see.

So if the only means to measure something is inaccurate, then... OK?

We've verified the accuracy of the method many ways. You yourself said 50 yard BC measurements were suitable for varmint bullets.

The accuracy of the 50 yard spacing is also double checked with a standard bullet that we have measured the BC of many, many times before. It comes up to within 0.5% of the same number every time.

And did this standard bullet pass thru the same portion of the chrono window as the other bullets?

The window issue is much less important given that we ensured that the planes were parallel and added mechanical rigidity. And all the bullets pass through an area less than 5% of the total window.

Courtney: All of our papers comparing original BC measurements with manufacturer specifications have used spacings more like 100-200 yards.

but any "useful" BC is measured over more than 200 yards.

Perhaps for shooting at 1000 yards, but not for understanding wind drift in 200 yard benchrest, predicting drops at 600, predicting wind drift at 600, comparing with data from different sources over similar velocity ranges, studying bullet stability, etc.

Sierra measured most of their BCs at ranges 200 yards and less, and many have found their BCs useful over the years. Would you call their data useless? Hornady measures most of their BCs at ranges of 200 yards and less. Would you call their data useless? Most of their AMAX and VMAX BCs are very close to your measurements.

And here's "the rest of the story".

Your low Mach number points were fired from reduced charges in standard twist barrels which does not produce the same RPM or stability condition as a bullet fired at standard MV and slowing at long range.

According to the JBM stability calculator, the lowest Sg represented in that figure is 1.607 under the firing conditions. I thought your view was that BCs did not experience significant drag issues for stabilities above 1.5. Were you assuming the bullet had a stability under 1.5, or do bullets have BC reductions for higher stability?

Our method for determining drag curves is basically the same as Sierra has used for many years. Pick a twist rate that ensures a well stabilized bullet over the velocity range. Fire 10 bullets at a number of velocities using reduced powder charges. Use the velocity drop determined from suitably accurate chronographs over a carefully measured distance, along with carefully measured environmental conditions, to compute the BC.

 

[Michael Courtney]

Yes, you're welcome for that by the way, it formed the basis of you're next several projects of USAF funded research on varmint bullets.

Most of the funding was private. The USAF allowed me to spend duty time on some of the varmint bullet stuff because they felt it was relevant to the mission. Don Miller wanted experimental data to serve the purpose of improving his stability formulas for plastic tipped bullets and hollow point bullets. The USAF wanted a way to compute bullet stability without PRODAS (expensive and time consuming). So for less duty time than requited for an AF engineer to run one bullet through PRODAS, we provided formulas and a spreadsheet to predict stability within 5% that most well-informed shooters can use. The USAF also appreciated the new method for measuring bullet friction, though they realized the Army cared more than they did. We used varmint bullets in that one because the M855 has much bigger manufacturing variations, though we did eventually measure the friction of the M855.

The USAF has periods when they care about marksmanship, and with all the old M16A1s (slow twist) in their training stocks, they wanted to evaluate and be able to predict the locations where the M855A1 would be stable from a 1 in 12" twist.

Frankly, I was grasping at straws to explain how your BC's measured over 100 yards might be so different from mine which were measured over 600 yards.

In retrospect I should have just said; your uncertainty is just more than you think.

But instead, I modeled a scenario in which 11 degrees of yaw might explain the difference between our measurements, now you're trying to use that against me.

I'm sorry you took it that way. I thought it was a good idea at the time and an example of one of our more productive exchanges over the years. It was a hypothesis that was well formulated and worth the experimental efforts we took to evaluate it.

I only brought it up because another poster suggested that pitch and yaw might be introducing error in our BC measurements. My purpose was to explain that we had given this possibility thorough evaluation and done due diligence in eliminating it.

Gain access to more than 200 yards worth of range.

Test some bullets that people actually care about BC's.

Then we might be able to compare notes.

Or you could measure the BCs of more varmint bullets. Seriously, had you measured the BCs of the varmint bullets and published the results, odds are pretty good your measurements would be very close to ours, and this thread would not exist.

Seriously, since now you know that we have attended to the plane and window issues on the chronographs, and since you know that we are tending to the stability issues, is there any reason why dual chronographs at 200 yards and under can't be effective using powder reductions to cover the velocity range (as pioneered by Sierra)?

At some point I bet you'll need to use a reduced powder charge to get drag curves down to M1.0 - M1.2 for those super high BC bullets. Stretching your acoustic method to cover the entire supersonic range of .743 and .818 bullets requires very high placement of the midrange microphones and wind drift puts the bullets at unknown distances from the midrange microphones, so you cannot correct for shock wave travel distance (delay time). Sure, with microphones out to 600 yards, you won't need as many reduced powder charges as we do but you might consider that one or two reduced powder charges is preferable to a 1500 yard microphone array.

At longer ranges, wind effects, changes in environmental conditions (Temp, humidity) over the range, and less accurate determination of distances rob most of the benefits of longer range. The reduced rate of fire due to management issues of instrumenting and shooting at a longer range would further diminish our ability to shoot 50-100 shots to establish a drag curve. We've got access to ranges with over 200 yards of room, we're just not convinced it is necessary as long as we can lower the velocity with reduced powder charges and maintain adequate stability.

 

[savagedasher]

Michael your telling me u used reduce charge. My gun will shoot 1'' of vertical if the speed isn't correct. My advice is go back and learn how to tune a gun. Larry

 

[Keith Glasscock]

The gentleman who posed the question had previously asserted enough confidence in the experimental method that he said he intended to repeat the experiment himself. His sudden assertion that proper friction measurements were impossible without pressure gauges helped me realize it might not be a short discussion. By the way, ARL didn't use pressure gauges either in their friction studies.

I had agreed that your data appeared linear for blue dot. That said, I suggested a faster powder that would decrease the difference in pressures as a result of the increased combustion volumes allowed if the commonly accepted theory of how lubricants work were true. My intent was to appeal to a real scientist to revisit a potential complete loss of validity as a result of a major assumption.

I wanted to rerun your experiment with an instrumented barrel in order to determine if you had any valid claims whatsoever in your paper.

Don't ever attribute my interest in your publication or agreement on one minuscule item within it as confidence in your findings.

On another note: What happened to having to send a CV, your personal residence, verification that you were a real scientist, NDA, a secret clearance, and all that other stuff? Now all one needs is to be a US person to get information?

I keep watching because I just can't stop. It's like a train wreck, you can't stop looking.

 

[Michael Courtney]

On another note: What happened to having to send a CV, your personal residence, verification that you were a real scientist, NDA, a secret clearance, and all that other stuff? Now all one needs is to be a US person to get information?

You wanted raw data which is covered by various confidentiality agreements and requires third party approvals.

We can and do provide method details that often get trimmed from a paper when editing for length. It is understood by all parties that when we get approval to publish an experimental method, details are not omitted for purposes of obfuscation, but that we will provide additional details needed for independent replication of our results on request by US parties. Want to know what software we used for analysis or the model of a sensor or the vendor of the HBN? Send an email asking and confirm you are a US party.

Raw data is a different deal. Raw data often contains scientific value beyond what was approved for publication. We prefer the enemies of the US not be able to draw all the conclusions from our data that we can. For example, the data we have is a pretty good road map to developing subsonic loads and evaluating their consistency. Raw data is proprietary and has competitive value for future research. Most scientists take precautions to prevent their data from showing up in their competitor's grant proposals. Raw data may also have value in future publications. We are considering publishing a group of our light load data as a resource for shooters and for laboratories who need light loads to study terminal effects in gelatin at reduced velocity, armor penetration, stability, etc. Some stakeholders do not want third parties publishing our raw data. On the other hand communicating load data privately runs some risk that the person getting it will harm themselves through misuse and attempt legal action against the provider. Much more consideration is needed before we send raw data to adequately address the above concerns.

 

[Michael Courtney]

Michael your telling me u used reduce charge. My gun will shoot 1'' of vertical if the speed isn't correct. My advice is go back and learn how to tune a gun. Larry

Blue Dot is awesome for reduced loads. Accurate. Predictable. Repeatable.

Google it. James Calhoun published the original results, but many report outstanding accuracy. We've had great success in .223 Rem and .222 Rem. No tuning, no fiddling, no farting around. Great groups first time every time. Weigh every charge on an electronic scale and you'll have consistent velocities also.

 

[284driver]

Michael, you're in over your head.

Let me guess, it's now time to move on to...

Child sacrifice! http://tech.mit.edu/V110/N50/jackso.50o.html

Or maybe this is just another 'rabbit hole'.
[/quote]

Haha, the Mattel bible thumping Ken doll. That's classic.

 

[tom]

Think about all the points I've dropped, and potential HOF points therefore. Thanks a lot Bryan! If not for you I would have been in TWICE. Now I have to rework all my 1000 yard loads for boat tail bullets.

Tom

 

[Keith Glasscock]

I really liked the insinuation several pages back that point losses in F-class due to windage were somehow relevant to the discussion of whether the BC numbers from a manufacturer were accurate.

Wait!

Michael, with a Kestrel and a measured BC, can I win in F-class?????

On the subject of Blue Dot, how does it overcome the harmonics of the barrel? What qualities in that powder reduces muzzle whip? I'll have to test that one... Might be my new go-to load for the 222 in benchrest.