The Russians were very poorly equipped to start the war. They had more men in uniform that they had long guns to equip them with. A lot of contracts for manufacture were given out by them in 1915-1916. They also bought a lot of obsolete arms, if ammunition was provided as well. As a neutral the US was well positioned to produce arms for whom ever had the money. And a lot of manufacturing companies tried to cash in, rightly so. But this was a double edged sword in that when things ended they had a lot of investment in materials and equipment that they had no market for. But for about four years there was a lot of money to be made.
I think the war ended six months earlier that the most "optimistic planners" expected. The US had just ramped up a huge number of Patterson Conversions for the 1903 that was to be the secret weapon which would win the war in the Spring of 1919. Whoops, it never got used and was shortly after the war all but completely destroyed. It was going to convert the bolt action into a walking semi automatic rifle capable of a huge number of shots as men advanced to break the trenches. The pistol round was limited but at close range would be impressive. I am glad it never got used because I do not think that the machine gun was going away and any advance across no mans land was still going to be brutally expensive. Once in the trenches it would have been a game changer.
