Grouse, I'd say it's you that acting like the "JR" here, seriously. People duplex smokeless and bp in low pressure cartridge guns all of the time. Does that somehow make the overall pressure more than the max pressure of the individual powders? not on your life. I would venture to bet that the TC warning against mixing powders is referring to mixing smokeless into the bp or sub since they talk about the danger of using smokeless right before they say it.
Also badmouthing CVA gets a little old; when was the last time that you heard of a CVA blowing up? The ones that I ever read about were from years ago and Randy Wakeman was the one broadcasting it. They sell thousands of rifles every year and you don't hear a peep about safety issues. They may not be made in America, but they obviously shoot very well and many people are very happy with them