If you are going to limit us to the 20th century.....
1. The 1895 Winchester Lee Navy in 6mm. Phased out in Rifle and Machine gun form around 1903 by the Navy and Marine Corps.
2. The 1903 Springfield Rifle in caliber 30-03. Only used for 3 years until they developed the 30-06 cartridge.
3. The model 1894 Winchester carbine in 30-30. Yes indeed it was used by US troops tasked with guarding timber reserves and in areas like Alaska for bear protection. I guess they figured the soft point 30-30 ammo was better than pointy hard-ball..
4. Remington model 11 semi-auto shotgun. (Looks like a Browning Auto 5) I don't know how many they bought, but I have one that is Army marked.
5. Pre-64 Model 70 Winchesters in 30-06 as sniper rifles. Ask Carlos Hathcock.
6. The M-6 survival rifle in 22 Hornet and 410 shotgun. The real ones made by Ithaca in the 1950s with the 14 inch barrels. Not the wannabe civilain clones.
7. The bushmaster aircrew semi-auto survival carbine in 221 Fireball. The civilian versions were in 223. The shorter barrel in the real gun worked better with 221 Fireball.
8. The Chauchat (cho-cho) machine gun that US troops were forced to use in WWI. It was in 8mm Lebel and a real piece of junk.
9. The Stoner AR-5 bolt action 22 Hornet aircrew survival gun adopted in 1956. Called the M-4 by the Air Force.
10. The Savage / Stevens over & under shotguns / rifles bought by the US Army Airforce as survival guns during WWII. Particularly for the Pacific area.
11. Stevens Model 416-2 .22 caliber training and marksmanship rifle. 10,338 purchased by the US. govmt.
12. Stevens 520-30 12 Gage Shotgun in Trench and riot configurations. 35,000 plus purchased by the US Gov.
13. Stevens 620A 12 Gage Shotgun in Riot config, 12,000 plus bought.
14. Savage 720 12 Gage Shotgun Semi auto, This is a "training gun" used to teach aerial gunners how to shoot at moving targets, similar to shooting trap or skeet. This semi-automatic model was based on Browning's patents, and was very similar to the Remington Model 11, and those made in Belgium by FN.
15. Savage Model 24 Rifle-Shotgun Survival Gun .22 long rifle and .410 shotgun. 1,900 bought around 1949. Were repalced later by the M-4s, and M-6s.
16. The Swedish K submachine guns. 9mm.. Numbers were purchased and used by special ops groups as were some Browning Hi-Power (P-35) pistols. I last saw a Swedish K being used by a Delta dude during Desert Storm.
During World War I, the Stevens facilities were turned over to "New England Westinghouse" who produced about 750,000 Russian Mosin Nagant rifles under contract for the Czarist government. After the Russian Revolution in 1917, the U.S. government purchased about 280,000 undelivered rifles from New England Westinghouse and Remington. Many of these were issued to training units but a few went to U.S. troops later sent to fight in Russia on the side of the "White Russians" against the Communist "Red Russians". The U.S. issued rifles are marked with U.S. style eagle and ordnance bomb inspector markings.