I spoke with the gentleman who built the first one, and coined the 6mm long dasher name.
He told me that it was because he took the neck / shoulder dimensions from a 6 dasher and dropped them on to a 6.5x47 lapua case, he was after a long 6 dasher case with more capacity.
Since the 6-6.5x47 lapua name was already circulating around he and Kiff dubbed it the long dasher, so there would`t be any confusion between the two.
I gave this cartridge a lot of consideration, but a .243 is right there in case capacity, and no forming hassles...if i wanted the 40 degree shoulder i`d just fire form it and be done, so i dropped it.
The small primer pocket could be reproduced in .243 or .243 AI with Palma brass, so that`s do-able as well....
Hope this helps,
Phil.