From Wikipedia
The Model 1855, which was the most widely produced revolving rifle, was available in .36, .44 and .56 caliber. Four barrel lengths were available: 15, 18, 21 and 24 inches. A six shot cylinder was used if the caliber was .36 or the .44. If the caliber was .56, a five-shot cylinder was used.
[10]
A revolving rifle used percussion caps, like revolving pistols of the time. A cartridge (consisting of powder and a lead ball) was loaded into the front of the chamber and then compressed with a plunger that was located beneath the barrel. Once the cylinder's chambers were loaded, percussion caps were placed over the vent nipples at the rear of the cylinder. The weapon was now ready to fire. In addition to being susceptible to chain fire problems, the revolving cylinder design also tended to spray lead splinters into the wrist and hand of the user.
[11] Revolving pistols did not suffer from this problem since the user kept both hands behind the cylinder while firing a pistol.