Just for curiosity.

*A-91: Soviet Union/Russia (1990/1991)

*AA-12: United States (1972)

*ACR/Bushmaster ACR: United States (2006)

*AF-2011: United States (2011)

*AK-47: Soviet Union (1946/1947)

*AK-74: Soviet Union (1972-1974)

*AKM: Soviet Union (1955)

*ARX-160: Italy (2008)

*Browning Automatic Rifle: United States (1917/1918)

*Blunderbuss Shotgun: Netherlands (18th century?)

*CM901: United States (2010)

*Desert Eagle: United States/Israel (1981-1983)

*DSR-50: Germany (1999)

*F2000: Belgium (2000)

*FAL: Belgium (1949-1953 for the original, ??? for the OSW version)

*FIM-92 Stinger: United States (late 1960s)

*Five Seven: Belgium (1990s)

*FMG9: United States (2008)

*Flame: Middle East (???)

*G36: Germany (1990s)

*Grenade Launcher: South Africa (1980)

*GT SIG 516: Germany/United States (Late 2000s)

*HK416: Germany (Early 2000s)

*Honeybadger: United States (???)

*Jack Hammer: United States (1984)

*KAP-40: United States (???)

*KL-40: Germany (2016/2017)

*Kar98k: Germany (1930s)

*KSG Shotgun: United States (???)

*L96a1: Great Britain (1982)

*Luger: Germany (Late 1890s)

*M-1 Carbine: United States (probably 1930s)

*M-107: United States (2002, modernized version of the earlier 1982 M-82 rifle)

*M-16: United States (Early 1960s)

*M-1911: United States (1911)

*M-249: Belgium (1984, modernized version of the MAG and known as MINIMI)

*M-3: Italy (Late 1980s)

*M-4: United States (1994, modernized short barrel version of the M-16)

*M-60: United States (1950s)

*M8a1: Germany (Late 1990s-Early 2000s)

*Makarov: Soviet Union (1946-1950)

*Metalstorm: Italy (Early 2000s)

*MK12 SPR: United States (1999-2001)

*MK14 EBR: United States (2000-2001)

*MK23/Socom: Germany (1990s)

*Model 1887: United States (1886-1887)

*Morano Thompson: United States (Late 1918s as the CHICAGO TYPEWRITER)

*MP40: Germany (1938-1940)

*MP5: Germany (1964)

*MP7: Germany (Late 1990s-2000)

*MP9: Switerzland (Early 2000s)

*MPX SMG: Germany (2013)

*P90: Belgium (Late 1980s)

*P99: Germany (1990s)

*PBP Shotgun: Italy (1998)

*PP90M1: Soviet Union/Russia (1990s)

*PSG-1: Germany (1968-1971)

*RPG-7: Soviet Union (1950s)

*SA-80: Great Britain (1976)

*SCAR-H: Belgium/United States (2004)

*Shipka: Bulgaria (1996)

*Skorpian EVO: Czech Republic (Late 2000s)

*SKS Sniper: Soviet Union (1945)

*Sten: Great Britain (1940/1941)

*Steyr AUG: Austria (1970s)

*TAR-21: Israel (Late 1990s)

*Taurus: Brazil (???)

*Tec-9: United States/Sweeden (1984)

*UZI: Israel (1954)

*UMP .45: Germany (1990s)

*USP .45: Germany (1990s)

*Vulcan Minigun: United States (1950s-1963)

*Vector: United States (2006)

*XM25: Germany/United States (Probably the 2000s)

- - - Updated - - -

I forgot the following:

* .840 Field Shotgun: United States (1947)

*Famas: France (Late 1960s)

*Greaser: United States (1942)

*Glock 18: Austria (1980s)

*Spectre: Italy (1980s)

*SMGPK: Pakistan (???)

*SMR: Russia (2009)

*SPAS-12: Italy (1979)

*SVD: Soviet Union (1963)