I have had revolver jams. On S&W revolvers, the ejector rod can unscrew and make opening the cylinder a serious challenge. A tight barrel-cylinder gap can cause a tie up if debris gets caught between the barrel and cylinder. Debris under the extractor star can make it hard to close a cylinder and prevent the cylinder from rotating. These are the failures I have experienced thus far, I know other failures are possible.

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VCDL, GOA, NRA