I have 2 I shoot BP in and have had others. I have never been able to regulate a BP double without resorting to duplexing. Perhaps some have but not me.
Having said that, if I were to acquire a new to me double in a BPE cartridge I'd have to try BP again.
A 5% leading charge of SR-4759 or 2400 with a commensurate reduction in BP has often done the trick for me.
Supposedly Swiss is the fastest but it wouldn't regulate for me. I almost got Olde Eyensford to work in a 43 Mauser....almost. I might revisit that powder as the weather warms. Fffg is faster than Ffg but I always start with Ffg....then try Fffg...then duplexing.
I have an abundance of Schuetzen BP and it works as good as any others when duplexed.
I'll be very interested in other replies.
