[Iowegan]

Lifemember, I have a similar 1858 Rem and I used to have a conversion cylinder. I sold the conversion cylinder for a couple reasons .... accuracy sucked, probably because of the twist rate that brnwlms mentioned. Further, it takes about the same amount of time to load and unload as the cap and ball cylinder. You have to remove the cylinder from the gun, unscrew the end plate from the cylinder, knock out the spent cases, insert fresh cartridges, screw the end plate back on and finally replace the cylinder into the frame.

Here's my 1858 Rem ASM:

 

[Iowegan]

The best powder is fffg true black powder but it has become almost impossible to find. 777 or Pyrodex is a decent substitute and works much the same as true black powder.

"Calibers" were measured different back in the day ..... it was based on the largest diameter rod that would fit in a bore. Today we tend to go with what's called "true bore", which is the bore diameter without rifling. For example, the old way of measuring bore diameter for a 357 Mag is .345", about .009" smaller than true bore diameter of .357". This difference is because of the thickness of the rifling that extends from the true bore.

When the Old Army first came out, it was listed as a 44 cal revolver but later in the game, Ruger called it a 45 cal because the true bore diameter (.45") is the same as a 45 Colt . To add to the confusion, pure lead balls need to be slightly oversized so when they are seated in the cylinder with the ram, it should cut off a little lead ring. This insures the bullet is seated tight in each chamber to prevent flash over The 1858 Remington was intended for .457" round ball bullets. After being "trimmed" during seating, they somewhat resemble a football and are very stable in flight. You can also use .452" "mini balls", which are round nose bullets with a hollow base, These bullets are notably heavier than round ball .... usually 250gr for 45 cal.