ronlaughlin
Have you played around with a TC Speed Breech Plug?
This plug when modified is an excellent BH plug and does not have the power pocket you speak of.
I do not think the powder poclet is the magic key - it is the modification of the flas channel as well as the flash hole.
I have modified several Knight plugs, an Omega plug with the vent liner on the nose. They work very well with any primer you shoose to use + plus they reduce blow back presures on the nose of the primer by offering a larger volume flash channel.
Here is a drawing i made that shows the modifications.
Lee has modified a Speed breech in a simular manner with excellent results. Lehigh has bult me several of this type of BP and we use them all the time with great results even shooting an old Remington 209-4 primer (a primer designed for 410 shot guns.)
I believe Busta has also made these same modifications with great results.
Here is a picture of a couple of modified CVA plugs - they work equally well ignitien BH with any primer, although they are not as clean as yours because I had no way of head spacing...
Just some additional thoughts from the peanut gallery...