Well had you noted the two rifles I showed and if you know about Pyrodex, then you would know that NEITHER of them will operate with anything but real black powder (of which I have plenty).
I'm not going to waste my time or anyone else's by arguing semantics of how BATF treats Pyrodex.
In terms of application it is a black powder substitute not a option to replace Bulleye, 3031 or RL 22 in any cartridges not originally designed for black powder. If you believe Pyrodex is no good, you are entitled to that opinion. Perhaps. unlike me, you have never used it in "modern muzzle loaders" like the TC Contender or Encore, probably never used the pellets or sabot bullets either.
Any honest unbiased analysis will tell you that they are superior to the traditional muzzle loaders we all love. Since Pyrodex works so well in modern muzzle loaders, there is no rational reason to assume it will not work as well in cartridge designed for black powder like the 45-70.
I asked for real world experience with duplex loading and got TWO on topic response.
The rest is the usual Internet "experts" running up their post count while not really being of any assistance.
Cast up and hardened a bunch of the 405 Lee plain base, lubed with SPG and loaded some with 2400/Pyrodex duplex and some with 4198/cornmeal. We'll give them a try tomorrow morning before continuing the search for the elusive atypical Antelope buck. Passed on seven good typical normal bucks so far but the season runs till 10/31 and the migration is very slow this year due to the mild weather.
Insofar as I'm concerned this is just a "fun" project", I'll keep those interested posted on results.