I've said it before and I'll say it again,
CASE DESIGN IS EVERYTHING!
I just finished working on a standard 6mm br with an 8" twist in a Krieger 4 groove barrel that is 26" long. I have also had a hand in or worked directly in load development on 4 6mm br improved's with like barrels and twists to the standard 6 br mentioned above. And from the data I have collected I can say one thing with absolute confidence.....the 40 degree shoulder on the improved version burns powder better period. ANd not just one kind of powder but all powders tried.
In the total amount of loads tried in the 4 improved's which numbers somewhere around 80 loads, there have been SEVEN loads that didn't produce standard deviations in the single digits! That is freaking amazing.
On the standard 6 br shooting exactly the same bullets and even the same lots of powder, it has had exactly 47% of it's loads produce standard deviations in the single digits. Of the loads that didn't produce single digits, 25, 30 and even higher SD's were found. The improved's seven loadsthat were not single digit were ALL under 20.
The proof is in the pudding here. That 40 degree shoulder vs the 30 degree shoulder is night and day when shooting heavy bullets with appropriate powders. Oh, and not to mention, the improved version shoots the bullet 100 fps faster on average with less powder on average too!
Now before someone jumps all over me for this comparison not being fair, let me just say this. I know that it was just one 6 br standard barrel being tested. But it was 4 improved 6 br's being tested-not just one. ANd of the four, they said the same thing. This case is efficient, is easy to load for, goes fast comparitively, and accuracy is top notch. The standard 6br is a good cartridge too but just not as good as the improved version for doing load development.
If it's not far, it's boring.