Thought I would make this to aid fanfictions that aren't very accurate as far as guns and such. I will post firearms that seem to be the most mistaken first, and clear up some major things about them that many people get wrong, not to point anyone out. I will also mention little-known facts about other weapons. Bumblebeeprime09(Talk) 23:34, December 15, 2010 (UTC)
The TAR-21 is an Israeli bullpup assault rifle. It uses the 5.56x45mm NATO cartridge, meaning it uses the same bullets as the M16, M4, ACR, G36, AUG, M249 SAW, and many other weapons. The TAR-21 accepts STANAG magazines, the same magazines seen on the M4 and M16 in-game. It is not used by the US or Russia, though it is manufactured under license in Brazil, and is used by the Brazilian Army, so it is possible that Militia people in MW2 have gotten ahold of TAR-21s, making their appearance not very inaccurate. It uses the MARS sight as it's standard optic, and is compatible with many types of scopes. It is compatible with the M203 grenade launcher.
The AUG is an Austrian bullpup assault rifle. It uses the 5.56x45mm NATO cartridge, same as many other weapons. It was designed in the early 1970s by Steyr Mannliecher (I apologize if this is misspelled), and was adopted by the Austrian Bundesheer in 1977, meaning it was a prototype before then. The A1 variant can only use the Swarovski scope, though the A2 variant has a Picatinny rail in place of the scope, meaning it can mount other optics. The A3 variant has a Picatinny rail system around the handguard area, so it can fit much more accessories, like the M16A4's rail system. It is used by mostly Austria and Australia (As the F88 AuSteyr). The only US branch that uses the AUG is Immigration and Customs Enforcement, whom are usually seen at International airports in the United States.
The FAMAS is a French Bullpup Assault rifle. It accepts 25 round straight box magazines, though later models also accept STANAGs. It is another 5.56x45mm rifle. It is only used by France and a few small countries around the Middle east and Northeastern Africa. It was designed in 1967-1971.
The PTRS-41 is a Russian Anti-tank rifle. It fires the 14.5x114mm round. The PTRS, unlike in Call of Duty: World at War, is not used as a sniper rifle. It is highly unlikely that it was ever used as an anti-peronnel weapon, especially a sniper rifle. Snipers would place a telescopic sight on their Mosin-Nagant.
The FN P90 was developed in the late 1980s. It uses a 50 round magazine, so it has a far higher capacity than other sub-machine guns. It is not used by Russia or the United States. The FN P90 fires the 5.7x28mm round, the same as the Five-seveN.
This was like the first repeating shotgun other than the double barrel. In 1936 production of this gun ceased and it isn't used by any official military forces anymore. Sorry. Even if someone uses it, your average soldier couldn't dual-wield it. The weight alone would break your wrist, and trying to spin-cock it would break your fingers.
The M14 is an assault rifle based of the famous M1 Garand. The M14 uses the same action as the M1 Garand, except it has a 20 round magazine and is a selective fire rifle. First produced in 1961 it was used extensively in the Vietnam War and continued in service to the present. The M14 has 16 variants, the most variants of any assault rifle in the world. The variant s are: Mk 14 Mod. 0 EBR, Mk 14 Mod. 1 EBR, M14E1, M14E2/ M14A1, M14M, M14 SMUD, M14 Tactical, M14 DMR, M39 EMR, Model 89 Bull-pup Sniper Rifle, AWC G2A, M21, M25, M14K, M1A, M14 SOCOM. The M14 is fitted for the 7.62x51mm NATO round.