[Hammerslagger]

When you wipe oil onto a cartridge case just before loading, or treat a chamber with oil or a similar coefficient of friction reducing material; you alter the normal distribution of pressure forces and abnormally increase the thrust and load onto the breech (bolt) face and the firearm's locking mechanism upon firing.

This practice may make for easier or more reliable operation of a firearm with mechanical problems (like a very dirty or rough chamber) in the short run, but doing so is almost universally considered to be bad (and/or potentially dangerous) practice.

Chambers and breech faces should be wiped dry of oil, with a tight patch, at the end of the cleaning process. Doing so will still leave enough oil in the pores of the steel to prevent rust until the next cleaning, under normal circumstances.