Of course it's best to contact manufacturer.
My real beef suggesting that these single shots can't handle full power smokeless loads is ridiculous. Today an modern single shot reproduction like a falling block should be able to handle anything you put into it. It SHOULD be able to seeing that this stuff mostly starts around 3k and goes up from there.
Really any falling block made recently should be able to outperform any nitro double rifle like 450 nitro express or 470. The single shot is an strong mechanism and metallurgical materials have advanced considerably since 1900 or 1930 for that matter. Just saying a Ruger no1 or an modern Sharp's or HI Wall should be able to run anything.
