I think you'll be very impressed with this particular round. I have a 6mm Dasher...which is an "Improved" version of the BR. Shooting a medium load as a fire forming load....I'm shooting @ 1/2 inch...5 shot groups at 100 yards using 105 gr. bullets...I have not had a chance to load up to the Dasher levels...but I'm more than impressed.
BTW, my chamber is designed with a .104" freebore and a 1:8" twist barrel with a length of 28 inches.