Inspect the mouth of the offending chamber under magnification. I'd be willing to bet you have a burr that is hanging up on the fired case. Since fired cases are slightly larger than unfired ones the problem usually is found only on extraction. Burrs can be very small so you'll need magnification. If you find one (they're not uncommon) a little gentle work with a needle file can work wonders. If you do, remove ONLY the protruding metal. I've seen two revolvers with this problem, a Colt Agent and a 696 Smith. After burr removal, both are still happily in service and function flawlessly.
Mark Lane to William Buckley: "Have you ever referred to Jessee Jackson as an ignoramus?"
Buckley: "If I didn't, I should have"