The phenomena of greased ammunition and cold soldered bullets appear to be reasonable DIY studies. There are hobby level pressure gauges that could give some real information instead of debates over what Hatcher said and what Hatcher covered up and what the Swiss used to do.
But as long as we are in ancient history...
I had a report on the British practice of "shooting wet."
Target shooters in England found that their .303s would shoot to a different POI in the rain, which is a common condition in the British Isles. Obviously the rainwater was affecting internal ballistics and the vibration that the Enfields depend on to compensate. So they took to dipping their cartridges in water on fair days. Their thinking was that they could not keep their rifles and ammunition dry in the rain but they could wet their ammunition when it was not raining and thereby use the same zero.
The similarity to oiled proof test alarmed some but this author concluded it was not a source of "broken receivers."
I have another period source that might discuss greasing but it will take some digging.
I figure that the Japanese machine guns had oilers because they did not copy the French Hotchkiss closely enough to include primary extraction.