Hey
HuntHard, I've often wondered the same thing myself - as I'm sure others have.
But its a I suspect there are a few smokeless powders that "could" be used in modern in-lines with the proper controls. But manufacturers would be crazy to talk about it. I've seen enough questions and confusion about powder and pellets on these forums to understand why. Add in a little confusion over volume vs. weight and the worms really start coming out of the can. For example, an accidental double charge of Pyrodex or Triple Seven will make a BIG boom and may hurt your shoulder or give you scope nose, but it's not likely to blow up your gun. A double charge of smokeless may well do so.
If you go to Hodgdon's reloading data center (
http://data.hodgdon.com/cartridge_load.asp ) and select
Rifle in the "Load Type" box and select
45-70 Government (Trapdoor Rifles)* in the "Cartridge" box, you will find a lot of low pressure smokeless loads. I'd guess the trapdoor rifle is a lot weaker than modern in-line muzzle loaders and that some - if not all - of those "starting loads" would be OK in an in-line. But I wouldn't try any of them without a LONG string between me and the trigger. Then too, beyond pressure there's the issue of the different way black powder and its subs build pressure, as opposed to the way smokeless does - the "pressure curve". I don't know what it is or how it would come into play, but I know it's there.
Even the Savage rifle is limited to certain powders.
Anyway, I would love to see the manufactures put some loading data out there. But they never will.