Timing question

[Morose47]

My gun is a Pietta copy 1858 New Model Army. My question is that after complete disassembly I have a timing issue. If I cock my hammer everthing seems to be O.K. but if I lower the hammer the cylinder rotates counter clockwise about 1/2 between the nipples. Any suggestions??

[Mainspring]

The Trigger and Cylinder Stop Spring might not be doing it's job.

If the gun is still disassembled then parts are not in place to do their job.