Glover,
THey are great chamberings. Not overly powerful for the larger 6mm bullets but they do work well and are impressive for their size. Other options that also work great in this class would be the 6mm Dasher and I really like the 6mm-250 which is a bit more then these. All are great.
Velocity is a bit low so in moderate winds, you will get a good amount of drift but they do pretty well for their size.
Main disadvantage to the BRs is that brass may not be around forever. Its already classed as sessional. The 6mmx47 Lapua may be an easier way to go, no fireforming needed and a bit more case capacity to get the velocity your looking for with less pressures.