AR15 22LR Kit, Sticky chamber.

[OkayShooter]

I purchased a older cliener/cmmg 22LR KIT. I was shooting it for the first time today. It was only -5 and using winchester wildcats. I would get the worst stuck case ever. The extractor would skip off, It would end up taking me pushing inwards on the extractor to get the case to come out, enough to get a small screw driver to pry it out the rest of the way. I had about a dozen of them. It was a clean chamber.

The 2 other rimfire pistols I had on the range didnt have a issue. Made me think it wasn't the weather. Cleaning it It appears to be elongated.

What would really cause a sticky chamber, when clean?

Thanks