This auction was enlightening for me for something other than the final price. Rock Island took excellent pictures, and I've saved some to my computer for reference. I never understood how Colt got away with timing the Walker so that the bolt would drop directly into the cylinder stop notches. Improvements to their later revolvers utilized a square bolt with square notches and included a leade cut into which the bolt drops (technically rises). This allows the bolt to pop up just before the cylinder finishes indexing and slide into the notch. By the time the bolt has reached the bottom of the leade, its leading edge is lower than the opposite edge of the bolt notch, which prevents (if everything else is set up properly) cylinder throw-by.
My Uberti Walker was set up originally to drop the bolt directly into the notches. It was peening the hell out of the opposite edge of the notch and was threatening to start introducing throw-by if I didn't cock it carefully. But I blew up those pictures of that particular Walker at Rock Island, and I noticed that its notches were very deep and cone-shaped. I've never seen an original Walker bolt, but I suspect its head may have been slightly cone-shaped as well. This may be why those originals were timed so precisely and why there are no bolt marks on that cylinder. There would be a lot of slop between the notch and the bolt as the bolt was first rising, but the two would eventually mate up well. And even if the cylinder had rotated slightly too far initially, the bolt would bring it back in line and indexing would be assured. My Uberti Walker has flat-bottomed, shallow oval stop notches with perpendicular sides and a flat oval-shaped bolt head with perpendicular sides. I made it behave by making the bolt release a tad earlier so that it hits the cylinder before the stop notch is directly lined up, but there is some drag induced when the bolt slides across the cylinder for those couple of millimeters. I'm going to be working on the bolt spring some to lighten it a little and reduce that drag. But I'm thinking that if Uberti made their Walkers like this original, this wouldn't be an issue at all.