.45 Long Colt is common usage for .45 Colt. Technically there is no .45 Long Colt. 44-40 has a bad rep for reloading but once you learn the ins and outs of it it's just as easy as anything else. Course you will lose some cases learning but Starline makes plenty of them.
The main thing is original 44-40 bores were .427. Modern 44-40's are .429 and most modern dies still size to .427, RCBS cowboy dies being the exception. So trying to stuff a cast bullet sized to .430-.431 into a case that's expanded to .428 doesn't work very well with the thin case mouth. You can use a .44 magnum expander plug or do like I do and use a punch to bell the case mouth enough. 44-40 was chambered in both rifles and pistols. .45 Colt was never chambered in original rifles. Jim hit the nail on the head when he said the thin neck prevented blowback into the action. It seals the chamber off very well. I use a Rossi 92 in 44-40 and leave a fired case in the chamber when cleaning the bore and no fouling gets in the action. Ballistically the 44-40 and .45 Colt are pretty close. 30-30 was never a bp cartridge and is an extreme bottleneck not suitable for bp. Not saying it can't be done but loading them with bp and getting compression on the powder would be difficult