as you rotate the cylinder to make sure a chamber is lined up correctly with the bore , put a bit of side pressure on cylinder making sure cylinder won't move outward.
Just as you should make a habit of doing on any revolver when loading as parts(including cyl. locks) wear out.
If the cylinder is not locked in place, won't it rotate out when you do what's in bold black? And won't the cylinder on a hammer gun do the same?
Again, can you quote any frequent problems revolvers have had in this area?