Daryl-

Lots of good info there.

The way I load my cartridges is such:
RWS percussion cap under the firing pin, tiny little dab of crazy glue on the firing pin at the rim, I throw the BP over that assembly then press a cupwad made from milk carton material in my special little bench made die set pushing the powder firmly with the sixteen bore rammer -- then I take specially made donut shaped quarter inch thick saddle felt wads soaked through with Wonder Lube paste, add a little more wonder lube in the hole in the middle of the wad, then press the roundball on top of the donut shaped wad.
From there I load them and fire them.

I make the saddle felt wads in the shape of a donut so as to have the pressure head against the powder and cup wad *expand* the outside diameter of the felt wad against the bore of the barrels. The roundball acts as a wedge, opening the ring of lubed felt. I find that with this arrangement the powder fouling is soft and I don't need to clean between shots.
I've tried it without the wonder lube and the results are like what you describe, hard caked powder residue.

I don't know if I'll be able to get the rifle out to shoot before the new year, I have a lot of work and some travel coming up (I'm in the middle of it!)
Once I get the rifle out again, I'll get the chrono out and see if I can get some MV times to post.

--Tinker