JohnKSa wrote:There's another reason not to lubricate the chamber. The brass is supposed to "seal" against the chamber walls at the instant that the gun is fired. For a tiny portion of time, the brass actually functions as part of the gun. That seal and the friction between the chamber and brass cartridge is good for the gun--reducing it will put more stress on the parts of the gun that lock the slide to the barrel.
The chamber should be clean but not lubricated at all.
I'm going to have to disagree, at least in part. While the chamber shouldn't be sloppy with oil, I don't see a real problem with having a slight bit of oil in there from a previously cleaning. On semi-autos, I don't think there's some super-tight seal created when firing that would be interfered with by a little oil residue. The cartridge has to be free to move rearward to extract and eject. In the straight blowback design (most SA pistols in 9mm Makarov and smaller), the rearward movement of the casing as it's fired is the sole force that moves the slide and ejects the empty casing. There is no barrel locking to interfere with in a straight blowback design. On a lugged/tilting design, I don't really see how oil is going to change the wear on the lugging, as the casing is pushing rearwards housing for the firing pin, which is attached to the slide. As the action of the slide is what is doing the work, and the movement of the cartridge is necessary for everything else to occur, I fail to see how a little bit of oil residue in the chamber is going to change things. Perhaps I'm missing out on some critical factor in the mechanics of a lugged barrel system. If so, please feel free to correct me.
All that said, if there is some slight extra wear factor associated with any oil at all being in the chamber, it would only last for the first round (or maybe two) before it's gone anyhow. I don't see how it would do any noticeable wear on a gun. You're likely to put more stress on the gun putting a mag or two of +P rounds through your gun every few months.
As for revolvers, non-SA shotguns, and bolt-action rifles, this would make no difference at all.