Changed Berger B.C.

[Marine sniper]

Thank you for this information, it will help to illustrate the magnitude of the change (if I understand it correctly).

For simplicity, let's just consider your 900 yard groups, which you noted were 3.03" low using the original BC of .631. Now 3.03" is very close for 900 yards. In fact, within a single 1/4 MOA click (two clicks would be too much).

Now, if you had predicted that trajectory with the newly adjusted BC of .616, the lower BC would result in more predicted drop. How much more? Assuming ~2800 fps, the difference in vertical POI at 900 yards is 2.9" using a BC of .616 vs .631. In other words, if you had generated your drop tables using the new BC, you would have been within 0.1" at 900 yards instead of 3.03".

Of course we're splitting hairs now, I'm just trying to show how small the required change is, and this one example shows that it is in the right direction.

-Bryan

Bryan,

I have to admit, as I was typing the info I was having the same thoughts.......since we are splitting hairs the velocity is 3000 fps.......now what about those 240's...... When is my 30-378 going to be sending those down range.

 

[jmden]

"now what about those 240's...... When is my 30-378 going to be sending those down range."

I can see we are going to have to send out a posse if Eric and Bryan don't get the big 308's and 338's out soon!

 

[Eric Stecker]

Regarding the 338 cal bullets we are gaining ground. We have three major challenges with the 338 cal. The first major challenge is the bullet design. We havn't made bullets larger than 30 cal so this is new territory for us. Fortunately, this is where Bryan comes into the picture. He completed designs for three different shapes in two different weights and we are very excited about their potential.

The second is to produce all the tooling as none of this tooling is shared from other calibers. At this point 90% of the tooling is received and will soon be tested.

The third major challenge is that we learned the machines we use now do not have enough stroke. To resolve this we are building a new machine. The good news is that we are not reinventing the wheel as this new machine is similar in many ways to our current machines just bigger. The bad news is that building a custom machine from the ground up is no small task.

We are about 40% complete with this machine. Once it is assembled the debugging process is impossible to schedule. We are working every day on the 338 cal project. I estimate that bullets will be coming of the machine in the summer of 2009.

Regarding the heavier 30 cal bullets, we have the same stroke length problem as we do for the 338 cal. Once the 338 cal machine is running well we will immediately go to work on making the heavier 30 cal. By that time designs and tooling should be ready to go. Don't hold me to this but we should have all these bullets in your loading rooms by the end of 2009 at the latest.

Regards,
Eric

 

[jwp475]

Eric, that basiscaly confirms what I had heard and that is the 338 bullets take a lot more PSI to form than do other calibers

 

[Forester]

The expertise of some commenting in this thread is way over my head but something about the exchange stuck me.

It sure is enjoyable to read an exchange between concerned customers and company representatives when the representatives genuinely care about both the quality of their product and their customers own area's of expertise. Quite a departure in comparison to most companies and in comparison to one notable thread in this part of the forum recently

Thanks Eric, Bryan and Berger Bullets as a whole!

 

[archdlx]

The expertise of some commenting in this thread is way over my head but something about the exchange stuck me.

It sure is enjoyable to read an exchange between concerned customers and company representatives when the representatives genuinely care about both the quality of their product and their customers own area's of expertise. Quite a departure in comparison to most companies and in comparison to one notable thread in this part of the forum recently

Thanks Eric, Bryan and Berger Bullets as a whole!

^^^^What he said^^^^^
Nice to be able to have a civil conversation with honest dealers!

Thanks Berger Bullets!
LeRoy

 

[edge]

Perfect!
I can circle July 1st on my calendar for the 300 grain 338 bullets

edge.

 

[Marine sniper]

Perfect!
I can circle July 1st on my calendar for the 300 grain 338 bullets

edge.

Yup, and July 2 on mine for the 240's !! LOL

 

[goodgrouper]

I appreciate the discussion, and am not angered by your statement. I would like to know what I've said that contradicts documented literature. I certainly don't want to be mistaken, and will correct my position if strong evidence is presented.



I can appreciate the accuracy of the old BC's, and I want to be clear that the 'new' BCs are not very much different. On average, the new values are only 4-5% lower, which for typical large caliber VLD's, equates to about 8 inches difference in predicted vertical impact at 1000 yards. Some of the new BC's are much less than 4-5% different, like the 210 VLD changed from .631 to .616. That's only a 2.4% change, and will only affect your calculated drop by about 4" at 1000 yards. Even with a very accurate rifle in calm conditions, this difference will be hard to detect. A 13 degree F change in temperature will cause the same difference.



I believe that the old BC's were very accurate, moreso than BC's for other brands. However, that doesn't mean they can't be better. Remember, we're only talking about a little change.



I understand that risk. I believe that even with the 4-5% reduction, Berger bullets will still have higher BC's than some other brands advertise, if by a smaller margin. After enough shooters miss targets because they're using BC's that are wrong, the value of an accurate BC will become apparent.



Our testing methods will continue to mature, and if it ever becomes clear that this was a mistake, we will correct it. For right now, we're putting out what we believe to be the most accurate number.



My testing procedure does use acoustic sensors, but it's not an Oehler unit. The sensors are placed in 200 yard intervals out to 600 yards. Rounds are loaded up and down to produce a wide range of flight speeds in 600 yards that simulates longer range flight. Occasionally, I do measure 'higher than expected' drag in the first 200 yards, but it only happens for the longest bullets, or bullets that have marginal stability to begin with; this leads to the next point.
You have a very good question about the yawing of the bullets. This is an issue that I'm currently investigating and learning about the effects of yaw on BC. At this point, I believe that a bullets yawing does not affect BC significantly for a normal length bullet that's properly stabilized. In other words, I have only detected unexpected reductions in the measured BC of the longest bullets for each caliber. The 90 grain .224 bullets are the biggest offenders. These long bullets are spinning plenty fast enough, but still experience a reduced BC that has to be related to the rifle it's fired from which makes it hard to state a universal BC for such bullets. However, I can say with confidence that all but the heaviest/longest bullets will not experience a reduced BC from yaw effects if properly stabilized.
If you have any information on this subject (which it sounds like you do) I would be very interested in discussing it.



If I'm thinking of the reports you're referring to, the conclusion (of BC's increasing very far downrange) has to do with the fact that the bullets were tracked to well below transonic speed where even the BC of a perfectly stabilized bullet would increase as speed got that low.

I'm very grateful to you for expressing your concerns about this issue. I take everyone's feedback very seriously, and will do the best I can to provide the most accurate data. I am confident that the current corrections to Berger's advertised BC's is a change for the better. If convincing evidence to the contrary is discovered, then we'll adjust to accommodate.

Thank you,
-Bryan

Bryan,

Thank you for your response. I have been anxiously awaiting getting back to the 'puter all day to see how the thread has gone.

In reality, if it's only a 4-5% reduction in BC, that would not be too bad. Most guns and/or shooters aren't accurate enough to split the difference at of a few inches at 1000 yards. But that box of 210's had me going! When my customer read me the bc off the box, I thought he had bought the wrong dang bullets! "It should say 6 something not 5 something" I told him. But he reaffirmed that it was a .5 something. It wasn't tell I pulled one out of the box and looked at it that I knew it truly was the 210 grain VLD.

And thank you for the explanation of the testing facilities. 600 yards would indeed be far enough to get an accurate measurement. And so, if that is what your getting, then I can swallow it. I guess my elevation (5000 feet) just simply happened to match the old BC's almost perfectly. Just for curiosity sake, what is the elevation at your range?

The tests I referred to just fyi were calculated throughout the trajectory from the bore to the transonic state and some went even beyond that. The basic result of the testing was to show how the longer bullets accentuate the yaw of repose over a longer distance and time. As I'm sure you know, every bullet yaws at it's first initial release of the muzzle including the short, little stubby bullets used in short range benchrest. They simply don't exhibit it for very long or for much distance and therefore are totally point on by 100 yards or less thus the great short range accuracy. But the long bullets just don't act that way at 100 yards or even sometimes 300 yards. Therefore, the testing ( the Aberdeen dopplar test in particular) showed that the bc of these bullets started out at "x" bc and then increased downrange, and then some of the bullets even went x-y in the transonic, then became x again in sub sonic states. But most just went up in bc until they leveled off then they hit the ground.

Anywhoo, good luck on the testing and by all means, please keep us informed!

 

[goodgrouper]

The expertise of some commenting in this thread is way over my head but something about the exchange stuck me.

It sure is enjoyable to read an exchange between concerned customers and company representatives when the representatives genuinely care about both the quality of their product and their customers own area's of expertise. Quite a departure in comparison to most companies and in comparison to one notable thread in this part of the forum recently

Thanks Eric, Bryan and Berger Bullets as a whole!

Boy, truer words were never spoken! Amazing how civil business can be sometimes. It's very refreshing!

 

[goodgrouper]

perfect!
I can circle july 1st on my calendar for the 300 grain 338 bullets

edge.

me2, me2! Of course, my barrel might be burned out by then damnit. Oh well, I guess I'll have to get a new one throated for the new Bergers!

 

[dmgreene]

Bryan have you done any testing on the 6.5 vld's yet? To make my drop charts work out I had to lower the 130's BC down to .575. I have also checked the measurements of the 130's against the 140's and other than the bearing surface being a few thousands longer on the 140's they appear to be identical. Is the BC of the 140 actually that much higher than 130s? (.595 compared to .640 for 140) And like the rest of guys said, thanks for the time and answered questions. This is the best reading that has been on here in a long time.

Thanks,
David

 

[BryanLitz]

GoodGrouper,
Thanks for the reply. Most of my testing is done in some riverbottom farmland in south central Ohio, at just a few hundred feet ASL. I note altitude, but use the actual temp, press, and hum of the day to calculate air density rather than assume standard conditions for altitude.
I will continue to study the yaw effects. It's a very interesting challenge because it might not be totally repeatable for every rifle. My original assessment is that there cannot be significant levels of yaw (enough to affect BC) because such yaw levels would cause tremendous dispersion. In other words, in order to get a 2% reduction in BC, there would have to be so much yaw that groups under 5 MOA would be impossible. (you can read a write up about this on my website:
Homepage of Bryan Litz - A Bravenet.com Hosted Site
Look at the "Ballistic Coefficient Testing" article linked on the left.
I may have to revise those conclusions because apparently, there can be a substantial reduction in BC without accuracy going completely to hell. I'll have to revisit the modeling to see what mechanism makes this possible.

David,
The new BC's for the 130 and 140 VLD's are (average from 3000 fps to 1500 fps):
6.5mm 130 grain VLD: 0.552 (just 4% lower than what you found)
6.5mm 140 grain VLD: 0.595

These two are being decreased about 7-8% from their original values, which is a large change compared to most others.

They are still the highest BC bullets in their weight class. For comparison, I measured the 142 SMK at .588, which is just 2% higher than their average advertised value.

The 139 Lapua Scenar measured at 0.557, which is 10% lower than their advertised BC (I think my lot of Scenar's for this test had a larger than average meplat).

The 140 Amax measured at 0.584, which is 6% higher than their advertised BC.

These BC's are completely consistent with common sense if you simply line these bullets up against each other and consider the profiles, and account for a few grains difference in weight.

The Berger VLD's (130's and 140's) were interesting because they had the exact same form factors (drag). This means that the difference in BC is completely do to the difference in weight between them. In other words, the 140 VLD is 7.7% heavier than the 130; and so the BC is exactly 7.7% higher. This wouldn't be true if the drag were different between the bullets but it is. Just an interesting note. The 7mm 168 and 180 grain VLD's are the same way.

-Bryan

 

[marc357]

Quote: "The .30 cal 210 BC of 0.575 is a mistake. The real value should be 0.616."

In order to get ExBal to agree with my real-world drop, I had to fudge the B.C. down to .615 (from the previously advertised .640 and .631)

Kinda satisfying to know I came to the same answer with my limited math skills, LOL

Marc