You hit the nail on the head Bill of Rights! Radial expansion is what prevents lug set back and other damage to the action. Once the brass contracts the brass is easily extracted, providing the chamber is as smooth as it should be and doesn't have any developing issues. In truth, the better polished the chamber and the dryer it is the longer it will endure hot rod bench rest and varmit loads, in other words, my type of reloading.
When I was a youngster about 45 or 50 yrs. ago, I blew the bolt out of my 22 B.A. (bolt action) rifle and learned at that time it was becase I had a habbit of putting a light coat of gun oil on the chamber. That was only a 22 LR, I can't imagine how much impact a high powered bolt face and lugs would have to endure from such a foolish mistake. My best friend's Dad at the time was a ballistic and firearm expert and he took one look at it and said " you oil the chamber before firing it didn't you?" If you have any doubt I strongly suggest you speak to someone that is qualified in this area, beyond a forum opinion such as me, and I assure you they'll rectify this very important fact. One particular method that they use in the UK for proofing firearms is one round fired from a "wet" chamber (oil) and then an over pressure dry round. The wet round is to test the lugs for required tensile strength. This simular method is also used by some firearm manufacturer's to find limits to what the lugs or the actions in general can handle. Of course they also use transducer's to know the exact psi being generated while they are trying to blow the action apart.
Any doubt to the importance of shooting the chamber only when it is completely dry and free of anything that could interfere with case seize, can be easily varified with any of the reloading components manufacturer's or firearm manufacturer's, Speer, Sierra, Hornady, Hogdon, Remington, Winchester, Taurus, Sako, and so on.
Imagine a cartridge producing from 20,000 - 65,000 psi slaming into the bolt face with all of that impact time and time again and you'll discover head space issues and worse, sooner than later.
Anyway, there is nothing wrong with oiling the action and other moving parts and it is a deffinite preventive to excessive wear, just don't get any in the barrel or chamber.