Mike Rowe:
Please do not "say no more" because your input is both thoughtful and based on your experience.

I would be curious as to your suggestion in the following situation:
Consider an unaltered antique/vintage BP Express double rifle that simply cannot be gotten to bring its right/left impacts together with straight Black Powder only loads. The assumption would be that the rifle was from a reputable maker and that it in fact did regulate well in the old days.

Now rather than trying "Nitro for Black" loadings to get it to bring its impacts together would you rather try sane and careful "duplex" loading to essentially preserve the advantages of Black Powder loading while potentially achieving suitable regulation?
I know full well that Duplex loading can have its own pitfalls if not done in a careful and informed manner.

Personally I think it unfortunate that Kik brand Black Powder is no longer….It did about better than any other in old BP Doubles.
- Mike Warren