Interesting figures for Dyer BCs but more info needed for making accurate tables. At what velocity thresholds do the BCs change or are the BCs an average figure.
Berger Bullets are about to revise their bullets BCs to reflect an average figure and posted this on 6mmbr.com just recently.
Quote from 6mmbr.com Forum posting.
http://www.websitetoolbox.com/tool/post ... id=3151552
I quote...
12/07/08 Reply #1
What's going on?
In a short time, you will notice changes to the advertised BC’s for Berger bullets on the box labels and website.
How was BC established in the past and why change?
Historically, Berger BC’s have been calculated using a computer program written by Bill Davis specifically to predict BC’s. The program takes the bullet’s design dimensions as inputs, and returns a predicted BC that’s acceptably accurate for a computer prediction (+/- 10%). Although the old way was ‘acceptable’, there is a more accurate way to determine BC; by actually test firing the bullets, which is how our BC’s will be established from now on. The experimental procedure and equipment that is being used to measure BC has been under development for over a year, and is able to produce results that are repeatable within +/- 1%.
How much will the BC's change?
On average, the new BC’s are a little lower than the old ones, about 4 to 5% on average. To put this in perspective, a 4 to 5% difference in BC equates to about 8 inches (out of ~300) difference in drop at 1000 yards for a typical long range round, and about 4 inches (out of ~70) difference in wind deflection in a 10 mph crosswind at the same distance. Some BC’s will change more than 4 to 5%, some will change less. Bottom line is that we believe the new BC’s are more accurate because they’re based on repeatable testing and measurement as opposed to computer predictions that are based on theory.
Should I care?
Target shooters shooting at 'known distance' typically don't care about BC for accurate trajectory prediction. Just so you can get on target, you can walk the rounds in with sighters. Target shooters care about accurate BC's more for comparison purposes, specifically wind deflection comparisons.
Long range hunters, tactical shooters, and any other application that involves shots at various unknown distances rely on trajectory tables generated using the bullet's BC. The more accurate the BC is, the more likely the drop chart will result in hits for the shooter.
It’s important to realize that the bullets themselves are exactly the same as they’ve always been. The designs haven’t changed at all. We’re simply using a more accurate way to establish the BC’s for the same bullets.
More details on the 'new' BCs
The new advertised BC’s for Berger bullets will be referenced to the G1 standard (same standard used for all other brands) and will represent the average BC from 3000 fps to 1500 fps, which covers the ‘typical’ velocity range that our bullets operate at. Of course, some bullets will operate slightly above or below that band, and minor inaccuracies can be incurred because of that. I chose to use one average value for BC rather than defining it in velocity bands (like Sierra does) for a couple reasons. First of all, many shooters misunderstand the velocity bands, and simply apply the high velocity BC for the entire trajectory (perhaps thinking the BC is related to just the muzzle velocity). This will obviously cause inaccuracy in a trajectory prediction, and misrepresent the bullet when comparing it to others. Also, not all ballistic software programs have the ability to define multiple BC’s.
Some Info on other brands BC's
Just for some context, not all bullet makers establish BC in the same way. Sierra test fires their bullets for BC, and reports different BC’s for each velocity band. I’ve tested many Sierra bullets for BC, and with few exceptions, my tests have been in very good agreement with their claims (usually within +/- 3 to 5%). In order to make a fair comparison between Berger and Sierra bullet BC’s, you have to average all of the Sierra BC’s for each velocity band, and compare that to the single Berger BC. If you only compare the high velocity BC given by Sierra to the average Berger BC, it’s not a true ‘apples-to-apples’ comparison. I believe that both Hornady and Nosler also test fire their bullets for BC, however, their advertised values only apply for high velocity (tests are conducted only to 100 or 200 yards I think). This makes it hard to compare them to the Berger number. I’m not sure how Lapua calculates their BC’s.
The effect of this change on 'Marketing'
We understand that slightly decreasing our advertised BC’s may affect how ‘attractive’ Berger bullets are to some customers who are impressed with high BC’s alone. However, the amount that our advertised BC’s are decreasing is so small that there are few cases where we change positions on the totem pole. In other words, if we had the highest BC before the change, we still probably have the highest BC, but maybe by a smaller margin. There’s also the accuracy of the other brands advertised BC’s to consider when looking at the totem pole.
To be honest, I’ve always hated the idea of BC being used as a marketing tool (although I can’t deny that it can be effectively used as such). The BC of a bullet is an important number that people use to analyze the performance of rifles, calculate trajectories, and hit targets. I believe that our new BC’s are more accurate, and will help shooters achieve better success which is what I think it’s all about.
Future Plans
There are plans to improve the way we represent our BC’s in the future that’s less tied to velocity which will clear up a lot of the ambiguity on the subject. It will be a challenging transition, and we’ll make it when we feel all the pieces are in place to give it the best chance of success. Until then, we feel that these experimentally determined, average G1 BC’s are the best way to go.
I am happy to address any questions or concerns related to this change.
-Bryan
__________________
Bryan Litz
Ballistician
Berger Bullets
...End of quote!
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