I have a Pietta exact replica M1858 Remmington New Model Army 44 caliber revolver with an 8" barrel and shoots a .451" ball. The 8" barrel is common to all the 44 caliber M1858 Remington New Army revolvers.
The Pietta reproduction of the M1858 Remington Navy 36 caliber revolver has a 6-5/8" barrel and shoots a .376" ball. Pietta also makes a M1858 Remington New Army revolver that with oversize frame and grips, 44 caliber, 8" barrel and uses a .451" ball. Target shooters prefer the oversize frame and grip.
The Uberti exact replica of the M1858 Remington New Army 44 caliber revolver uses a .454" ball. Pietta also make an M1858 Remington New Army 44 caliber "shooters" revolver that uses a .457" ball with progressive rifling.
On black powder firearms, the barrel length is proportional to the caliber (bullet weight) and amount of powder charge needed to achieve a prescribed muzzle velocity. Typically, the M1858 Remington New Model Navy 36 caiber revolver uses 18 gr. FFFg black powder with an 6-5/8" barrel and the M1858 Remington 44 caliber New Model Army revolver uses 22 gr. FFFg black powder with an 8" barrel.