For fun let's say the US Army and/or Marine Corps look at the Remington Model 8 in 1910 with its .35 Remington and 15-round special magazine (standard is 5-round box magazine) and decides they like it. The cartridge has a power roughly 90% of a modern 7.62x39/AK-47 round, but in this case they can fire in true semi-automatic fashion. What effects, if any, does this have?
The effect would be chaos. Congressional investigations, in fighting between high ranking Officers in both services. Massive negative PR campaigns by the, Springfield Armory, the NG, NRA, Winchester, Colt. Officers will be retired, and reduced for this.
Adopting that rifle would require a complete change in the views of military marksmanship held by both the USA/USMC, the National Guard, NRA and other civilian rifle clubs.
Somehow you would have to get rid of the importance of national matches at Camp Perry, because that was the main "event" most US service rifles were really designed for. Also the USA would have to draw the opposite lesson from its experience going against the Spanish Mausers in the Spanish American War. Finally then you would have to think of a way to get the military to give up on the 1903 Springfield rifle, the 30-06 round and all the machinery at the government armory and ammunition arsenals that make other items.
How would you convince them to give up on the modern spitzer bullet design for the round nose of the .35 Remington.
Also you would have to redesign the rifle to take the detachable magazine as the Model 8 use a fixed 5 round magazine fed by chargers.