UPDATE
As I live and breath I would never guess I would be today, holding the little .38 RF test kit in my hand today that Skeetex(mike) put me on. I ordered them Monday night from Luxemburg, Belg and they were on my doorstep today.
In reading the info on their website, almost any BP is good for the rifle cases. Surprisingly even ffffg powder. I would have thought that it would have been too fine. I don't have the Flobert 6mm blanks yet but I can make a primer with a .22 LF. The biggest thing they stressed on their site was to make sure I filled the case completely.
So thanks to several here and Mike, I will be able to shoot my Rem #2 .38 cal RF roller tomorrow for the first time.