Doesn't need and won't take a washer. Passed test #1.That test is not a reliable test. Most open top revolvers won't even go together if they're "out of line" (because of the broaching process) so the only test is a small washer in the arbor hole and assemble ( if you can, why can you ?) Or drive the wedge in (don't be a weenie!!) and see if it locks up the cylinder.
Cylinder not locked with wedge all the way in. Passed test #2.
Arbor and arbor hole lightly sanded, polished & lubed so gun can be disassembled without need to use ball peen hammer.