I can give you another example of oiling ammo. I was working with some Germans at the tank range and checking out a modified MG-42. In the turret is thousands of rounds of ammo linked together. They (Tank crew) pour oil over the belts to keep it feeding right. If you ever heard a .308 MG-42 you know why they oil the ammo. This gun uses a different type lockup.
When it comes to added thrust against the bolt of a locked rifle, I do do believe it increases as the chamber gets more of a polish or has additives to make it smoother.