My personal take on the US's firearms
Pistol:
Colt 1911A1 .45
Luger 1907 .45 (Taken for Testing, privately purchased sidearm of Cavalry officers)
Colt 1876 .45 (classic cavalry 6-shooter)
Rifle
Springfield M1903 30-06 (Licensed copy of Mauser Gew.98)
Springfield/Krag-Jorgenson M1898 (licensed copy of the Krag 1892, used by rear-line personnel)
Winchester M1895 (Black-Powder Lever-action, used by reserve personnel and security forces)
Browning M1918 30-06 (automatic "Trench assault" Rifle, produced in limited numbers)
Submachine Gun
Thompson M1928/1928A1 .45
Springfield M1930 9mm (Licensed copy of German MP-28, Issued in limited quantities to US Marine Raiders)
Winchester M1933 9mm (Licensed copy of Suomi KP/-31, 2800 built, Production run issued to Quebec)
LMG:
Winchester M1942 30-06 (Licensed copy of MG-42, used to counter CSA's Model 1934)
Browning M1919 (Tripod-mounted Support MG, based on Browning M1914)
Browning M1895 (Reserve weapon)
HMG:
Browning M1914 30-06 (Watercooled Machine gun on heavy mount)
Browning M1923 .50 (Heavy anti-material Machine gun)
Other:
M48 "Home Run" 30mm Rifle Grenade launcher, made from a modified Flare launcher attached to a Springfield.
M1944 "Barrel Bruiser" Shaped-Charge anti-Barrel rocket launcher, based on German "Panzerfaust" Never saw action due to the end of the war.
Winchester 1897 "Trench Gun" 12-gauge Shotgun.
(point in fact, there IS a .45 Luger, and the US did attempt to make an MG-42 copy in .30-06)