I hate loading the 1860 Colt army revolver. The 1851 Colt navy revolver has a stop on the LH side of the barrel frame that prevents the cylinder from over-rotating after you install the ball. If you accidentaly rotate the cylinder of the 1860 Colt army revolver slightly past the ram, you cannot turn the cylinder back to align with the ram. Then you must completely disassemble the 1860 Colt army revolver and reinstall the cylinder in postion that you can rotate to a position that will accept the ram.
The stop on the LH side of the barrel frame of the 1851 Colt navy revolver stops the ball sticking out of the cylinder and prevents the cylinder from rotating past the ram.
I look at every revolver before I buy one to see if the frame is wide-open in front of the cylinder. I have noticed that the 1860 Colt army revolver is the only pistol that is open on both sides of the cylinder and does not have the handy stop on the LH side of the barrel frame.