The "greased ammunition" issue arose as a result of the "tin can" bullets issued at an early stage in the development of bullet jackets. The material used had the reputation of creating serious metal fouling. The solution to the problem was to lubricate the bullets in loaded ammunition with commercial lubricants, which inevitably found their way onto the mouth and even the body of the cartridge case. This caused two different problems, both potentially serious.
First, coating a cartridge neck with an incompressable substance inhibits the expansion of the neck when the cartridge is fired, duplicating, in effect the problem caused by firing an oversized bullet.
Secondly, lubricating the case body interferes with the ability of the case to obturate and adhere to the chamber walls, resulting in a percussive blow to the bolt when the case if first pushed forward by the firing pin blow and then slammed back against the bolt, when the case fails to cling to the chamber walls. Either could cause a destructive event.
