JDT - you should enjoy those rifles.
I acquired a M1893 action a few years ago, when Numrich still had factory Marlin M1893 barrels. I ended up with a 26" half octagon Black Powder barrel. I've needed to do some research on it. Here's the story as I understand it.
There's a lot of confusing information on the BP versus SSS barrels, and we probably need to consider the Winchester and Marlin stories in parallel.
For Winchester, release of the .30-30 had been held up due to barrel wear issues with jacketed bullets and smokeless powder. This was with their normal barrel steel, the same as used for the Model 92 etc into the 1930s (see Cinnabar video). These wear issues were resolved by the use of Nickel Steel barrels, marked "Nickel Steel", which became standard for .30-30, .25-35 and .32 Special. NS barrels were offered as an extra cost option for .32-40 and .38-55. The non NS barrels had no special markings, and when Winchester came out with the .32-40 and .38-55 WHV rounds (about 1600 fps) with smokeless powder and jacketed bullets there was no safety restriction on which barrels they could be used in.
Marlin approached the matter differently. For .30-30 etc they used what was probably the same Nickel Steel and called it "Special Smokeless Steel". As for Winchester this was offered as an option on .32-40 and .38-55. These rifles had case hardened receivers. The non SSS .32-40s and .38-55s were offered at lower cost with blued receivers and the standard steel barrels, labelled "For Black Powder Only". This appears to have been a marketing move to pressure buyers into the more expensive SSS model. I cannot find any evidence to suggest that these barrels were anything but the same (non NS) barrel steels that Winchester and everyone else were using, and for which Winchester was quite happy to provide the WHV ammunition.
My conclusion, for my purposes, is that my BP barrel is just fine with modest smokeless loads and cast bullets. Sustained use of jacketed bullets might accelerate wear. If I needed to (which I don't) I might test my luck to 1600 fps. Since you have both BP and SSS versions you can do all your serious stuff with the SSS barrel.
Others please chime in and correct any errors.
As for loads, my rifle is exceptionally accurate with Lyman #32359 120 gns with 4.5 gns Red Dot, 1050 fps. It also shoots well with bullets from the old WRACo 32-40-165 mould. Another 1/2 gn powder will get about the same 1050 fps velocity. Pistol primers in both instances.
ADI lists loads for 2205/H4227 (if you can get it) with 200 gn cast bullets at about 1350 fps, but the 1:16 twist is just a whisker too slow for the heavy bullet at that speed.
Another option is to start with a Loverin style bullet .314" and patch up to .321" with Onion Skin. Forget the gas check. The patch tucks nicely around the gas check shank.
I have made all my cases from .30-30s. If you think the cases are too short for what is supposed to be a 2.125" chamber, then standard .30-30 are also too short for my 2.120" and 2.150" .30-30 chambers.
You are only as good as your library.
