Remember, those 'fast powders' are often shotgun powders. Look how many rounds they get through them.
You can do pressure vs load graphs to visualize the whole deal, or just build decent loads at Level One ('trapdoor Springfield) and not overthink it or re-invent the cartridge. You wont likely wear the gun out in your lifetime like that, especially with cast bullet loads.
Fair point. I guess you could almost argue a 45-70 is something like a .410 rifled slug barrel, LOL! What with it being a straight walled round.
Have to admit the economy of using the trapdoor level Unique or 2400 loads you see in some of the old time manuals catches my interest.
I'm not really out to re-invent the cartridge, to be honest. What attracted me to it was it's ability to get the job done without jacketed, gas checked or paper patched bullets. Simple, plain cast was the attraction.
So probably nothing beyond roughly 1400 fps. for me, and keep to realistic ranges for those velocities. I'm thinking of it more as a .44 Mag - Super Heavy Bullets, than trying to make it compete with .30 cal rifle velocities. For me a trapdoor carbine would be fine, if one could be had for such a low price.
Old story from when I was a kid... a guy pulled into the range and had a crate marked 7th Cavalry... apparently some Springfields meant for Custer... who crate + the tools they sent with them. Have wanted a Trapdoor ever since I saw those... been probably 40-45 since then... still ain't got one, LOL! Ruger #3 as a second and probably better choice. I like that they aren't as fancy as the #1's. A shame they are out of print. (Don't know what's wrong with this industry anymore... they keep dibbling with great old designs or they drop them altogether...guns didn't used to be subject fads as much as they seem to be now.)
Someday, someday.
Though of course... I guess you could argue Trapdoors were proven obsolete at Little Big Horn,