Varmint Al's web page gets into a painfully detailed discussion on chamber friction and bolt thrust, but isn't an exact match to your situation of a standard chamber with oil. Interesting reading, though.
http://www.varmintal.com/a243zold.htm
As you oil the ammo or chamber, and reduce the friction between the brass and the sides of the chamber, the bolt will have to bear more of the strain. As long as that force is within the range the bolt was designed for, the rifle won't care. The .mil weapons designs are overbuilt to allow the rifle (or MG) to withstand the worst case without issue, so an increased bolt load isn't going to bother them. As you get closer to the limits of the bolt by changing to a different cartridge (for instance) with a higher bolt thrust, the friction between the brass and chamber becomes important.
I know I've seen how to calculate bolt strength somewhere out there....
ETA: Lilja, should have guessed.
http://www.riflebarrels.com/articles/custom_actions/bolt_lug_strength.htm