Brent, I know it is done and will continue to be done. I believe there is no part of a shotshell with a conventional wad that approximates dacron or floral foam over a relatively large air space. Even when shotshells use wadding, there is no load that I am familiar with that has a significant air space that a wad accelerates across before it encounters a stationary shot column. I understand some wads have a crush zone that may be largely air, but that is an engineered control feature not a potential air hammer.
I certainly believe that you have consistent, long term, excellent results with those fast powders, but would you use the same loading technique with 5744 in a BPRC? Though it wasn't mentioned, my suspicion is that the goal is to approximate original ballistics with slower smokeless powders that will not fill the types of cases that are probably being considered. If I had to guess, Unique or 4227 may do for reduced loads, but not likely to approximate traditional full power double rifle loads. But, I'm sure there are exceptions that I'm not aware of.
