I just got my GP100 back from the local gunsmith. It wasn't indexing well and it would not fire about every fifth or sixth time. The problem was a carbon buildup on the face of the cylinder, and a little high spot that he stoned down. He said about .001 in. high. I had lightly cleaned it with a patch and Breakfree CLP. He also sold me a cleaning cloth to use to keep it clean. He told me that Rugers have tight tolerances around the cylinder. I believe him.