I have a Remington .44, 1863 production, converted to 44/100CF about 1868.
They used the original cylinder, sawed off the back end where the Nipples were and sweated on a Plate with a new indexing ratchet machined into it. This means that the original muzzleloader cylinder is still in use, so it is straight-bored full-length, not chambered at all in the way we think of it. I swear, you can almost dump half a dozen .45-70s down there!
Just something to watch for.