Stainless galling
Galling is basically the material welding together under the right combinations of pressure, friction, and temperature. Certain types of stainless when used together are particularly good at it. Type 304 stainless when used against itself will gall very easily. To prevent this, if you are using a fastener in 304, then get a fastener made out of 'Nitronic 60' (UNS S21800), commercially available and a little pricey. Or you could get them in '17-4 PH', even more pricey.
As for lubricant, a couple that haven't been mentioned are 'Neo-lube' and 'Never Seez', both excellent stainless lubricants, though I don't know how they would be for firearms.
Hope this helps.