Patch700 is right about having a wet chamber. A minor amount or a light film in the chamber won't hurt anything I don't think. But if it has a thick film of oil or grease in it you can have major problems. This keeps the brass from being able to grip the chamber wall which induces more bolt thrust on the locking lugs. Like I said, if a small amount were left behind, like a light film, I think it can still grip the chamber wall enough not to cause any problems. If not, I think you would hear about a lot more shooters damaging their actions, or hurting themselves, or worse. But indeed a thick coating in the chamber is a big no no as the case won't be able to grip the chamber wall.