1. The FN FAL is a selective fire rifle, this makes it fully automatic (I thinks)
2. The L86 LSW is the A1 version, this version was pulled out of service and wouldn't remain at the time the game is set in. And it would be impossible for the Spetsnaz to gain control of them as they're only issued to the British Army and Cadet Forces
3. A Barret M82 would be extremley heavy and hard to sprint with.
4. It would be impossible to fire a Javelin from a standing position without your spine curling over from the kickback.
5. The Glock 18 isn't a machine pistol, it's a semi-automatic handgun used by law inforcement units.
Anymore you want?
Edit: I can go on about the LSW so I'll leave on 4:
1) BIGGY! It's not an LMG, it's a Assault Rifle, just with a longer barrel for increased accuary.
2) The barrel is completly different. On MW2, it's just a big black tube, but this is how it actually looks
[spoilers]
[/spoilers]
3) The magazine used is hardly issued to soldiers to them being about £120 each.
4) Finally, the SUSAT scope in MW2, is completely different to the one used in service by all forces (RM, RN, RA, TA, RAF)
(Btw, I'm an UK Army Cadet, that's why I know all the stuff on the LSW)