I guess when Uncle Sam is paying for rifles and parts (and winning scores) then part longevity is a secondary concern. I think it was the Air Force that tried the relief hole modification in the gas port of the M14, but I don't know if it was just a few rifles or if it was a standard modification for their service rifle team or a "one off" they tried. Somehow that modification is still legal in the books, but my memory isn't as reliable as Google anymore.
Good point about those small ring Mauser actions. I had a K.Kale Large Ring Small Shank Turk case hardened (the gunsmith I had do the metal work had it sent to a machine shop that would work on receivers) simply because those Turks had very tough steel, but almost universally suffered from poor heat treatment. That ended up a very nice 9.3x62 that I have full confidence in. With the small shank diameter I didn't trust it with a magnum brass diameter.
On the other hand, Kimber imported some Swede actions and proofed them for 308 loads and sold them on the American market. I haven't heard any horror stories yet about those rifles, but I have seen photos of Swedes that went "kaboom" due to hot loads.
Machine guns are awesome until you have to carry one.