6mm BR and 6 Dasher
The "improved" 6 Dasher case moves the shoulder .10" forward and shortens the neck by about the same amount. Additionally the shoulder angle is changed to 35 degrees. This all increases case capacity by about 4 grains. You get an extra 125-140fps with 105gr bullets for the effort, along with the added expense of custom dies. Dave Kiff at Pacific Tool & Gauge
has the 6 Dasher reamer.