NO manufacturer I've ever heard nor the US military says to oil your ammo or to squirt it into the chamber...that should be a clue.
But in the spirit of open mindedness, if someone wants to provide a reference, I'd be interested in reading it.
Maybe not the US Miltary today, but it was common practice
in military days of yore. This was just one
of the systems using a actual oil-pump system:
Schwarzlose machine gun has a device for oiling each cartridge to ease the reloading cycle.
On each stroke oil was squirted into the firing chamber to lubricate the incoming cartridge case.
Schwarzlose Machine Gun M1907
Honest, guys, it does no harm -- and can actually save the day. That said, good ammo/good chamber doesn't really "need" it. But rough conditions up and shoot marginal ammo.....