Hi Mark, good for you! Before you shoot your new 1851, measure both the bolt thickness and cylinder bolt slot width. A common problem with the Pietta 1851 and 1860 is that sometimes the bolt doesn't fit well in the cylinder bolt slot. There seems to be a tendency where the Pietta bolt is wider than the cylinder bolt slot. That causes the edge of the cylinder slot to get buggered. If you don't have a way to make those measurements, remove the bolt and test if it easily goes into the cylinder bolt slot. If the bolt is too wide, a little stoning of the bolt edge will bring it into correct dimension.
Regards,
Richard