Boy did I start something. The chrome moli barrels that most are making are heat treated to 28-32 on the Rockwell "C" scale. Most are stress relieved after the button is pushed through but not at a high enough temp to take the hardness out. This hardness is harder than the steel wool. The 50 BMG has a stelite chamber and the first couple inches of the bore on most, no stainless. I was not aware of any stainless machine gun barrel, most are way harder than commercial barrels. Some of the 300 series stainless is much harder but will work harden even more making them unsafe. The 416 stainless machines very nice, maybe that's why they use it.
In 1895 Winchester came out with their nickel steel barrel for the new smokeless powder 30-30 and 32 special. The barrel for the BP cartridges was not very hard compared to the new steel. Marlin barrel were marked "special smokeless steel". Mauser barrels were even harder.

I used to use a product from Herters called x ring paste,   found out  that it is boniami and 20 w non detergent motor oil.  still use it