Sorry, it's been awhile since I've had the time to investigate the issue.
First of all, the gun I have is a 15-3, not a 66. My apologies for the error. This is the first S&W I've owned.
After looking with a magnifying glass and using a flashlight to check out the one chamber which was causing the problem, I was not able to see any burrs, fouling, or other issues which could have been causing the problem. I tried cleaning the chamber several times with Birchwood Casey gun scrubber, which didn't do the trick.
So, with some hesitancy, I pulled out all of my Dremel tools. Relax, I wasn't planning on using the rotary tool to "route" the cylinder. I did find that I had a very fine grit grinding wheel which just fit into the bad cylinder. I put some honing oil on the wheel and BY HAND, moved the wheel in and out of the cylinder, being as careful as I could to keep the grinding wheel parallel to the cylinder walls. I did not rotate it. I was also careful to stay only in the back side of the cylinder as that is where the cases began to stick upon extraction. After a couple of minutes of carefully using the grinding wheel, I tried inserting a fired case. It went in a little easier, but not as easy as the other chambers. I put more honing oil on the grinding wheel and continued. After about 10 minutes of work, I was able to insert a fired case into the bad chamber just as easily as the good chambers. I took the gun to the range, and it worked just fine. I realize I was taking a chance here and I probably wouldn't recommend this to anyone else.
"If you love wealth better than liberty, the tranquility of servitude better than the animating contest of freedom, go home from us in peace. We ask not your counsels or arms. Crouch down and lick the hands which feed you. May your chains set lightly upon you and may posterity forget that ye were our countrymen." Samuel Adams.