Muzzleloaders, be it handguns or rifles must be loaded with Black Powder or BP substitute like Pyrodex. No Nitrocellulose can be used there.
So-called Nitro for Black loads were developed for loading old black powder cartridges with NC powder. There are also loads available for this, loads that must be strictly followed because BP rifles are not always intended for the high pressures developed by using NC powder.
Cordite is a triple-base NC propellant so that all weapons that are regulated with it can also tolerate our modern NC powders. The question is with which loads. The safest way is to follow the current loading data, which are available for almost all old nitro cartridges. Almost all authors prefer to use slow-burning powders. You can use fast burning powder like the IMR 3031 in the same load as the original Cordite load, but in most cases you need a filler because cartridges that were intended for the Cordite strands have a lot of case volume. However, the use of fast burning powder is controversial discussed and rejected by many because it is considered dangerous. Nevertheless, I did it and it works better than some people think. I also fired Cordite loaded cartridges in my old double rifle caliber 577 Nitro Express, but I don't recommend anyone to use anything in particular, especially and for a lot of reasons not Cordite loaded cartridges. Everything has to be done at their own responsibility as no one knows in advance in what condition all of these old rifles are, in in particular Cordite loaded ammunition.
It is recommended to read the book SHOOTING the BRITISH DOUBLE RIFLE by Graeme Wright as it is one of the best book when it comes to loading and shooting Nitro Express cartridges with double rifles. I load the cartridges 577 Nitro Express and 600 Nitro Express. Initially I had a lot of problems by reloading, but thanks to this book I was able to solve some of them. Unfortunately the books are extremely difficult to find.
