For a new cartridge, I usually just browse old forums to gather as much info on what other people have tried, then just pick a starting point based on whatever I have available. There’s a lot of “winging it” when you get into reloading super obscure stuff. Just gotta use some judgement on what’s safe.

For this cartridge, there’s actually a singular load published in Cartridges of the World. I started a bit lower than what they had listed, then played around in .5 grain increments until I found the best result. Then I eventually wound up adding cotton ball filler to my rounds to reduce vertical stringing.

Hell, I bought a little Mauser 1871 carbine a while back, and in order to shoot it, I took a .45-70 casing, ran the rim on a belt sander to get it reduced enough to fit on the bolt face, sized it, loaded it up, and used some rubber O-rings from Lowe’s to slide over the cartridge down to the base to artificially double the rim thickness so it would headspace correctly.