Well just to clear a few thing up that isnt the m4 it may possibly be the kar-15 like he said or the colt commando which was an earlier version of the m16...and the reason the ak is in mw2 is because it is a very reliable gun and cheapp so it is still primarily used by the less funded factions(russia, talibin, other militias) and the funny thing is that we gave the taliban their wepaons to fight another country yet when it was all said and done it was turned aroun on us...i wouldnt be suprised to see a FN Fal (Fal) which was an older veitnam age gun by some countries and shot fully auto(for all mw2 players) here is a list of some very considerable weapons
Chicom Type-56
Chicom Type-69 (RPG-7)
D-20 (M1955)
Kalashnikov AK47 (AK-47)
M-46 (M1954)
Makarov PM
MAT-49
Mortar, 81mm
PPSh-41
Recoiless Rifle, 75mm
RPG-2 Rocket Propelled Grenade
RPD General Purpose Machine Gun
RPK General Purpose Machine Gun
SA-7 "Grail" / 9K32 Strela-2
Simonov SKS
Tokarev TT-33
Type-24
Browning M1917 (Model 1917)
Browning M2HB (Heavy Barrel)
Colt / AAI M203 Grenade Launcher
Colt Commando (XM177E2)
Colt M16A1
Colt M1911
General Electric M134 Minigun
Hughes / Raytheon BGM-71 TOW
Ingram MAC-10
Ithaca Model 37 Featherlight
Ithaca Model 37 Stakeout
M1 Carbine
M1 Thompson (Tommy Gun)
M1A1 Pack Howitzer
M20 Rocket Launcher, 3.5"
M60 General Purpose Machine Gun
M67 Recoiless Rifle, 90mm
M72 LAW, 66mm
M79 Grenade Launcher
Mortar, 60mm M19
Mortar, 60mm M2
Mortar, 81mm M1
Remington Model 870
Rock Island Arsenal M21 Sniper Weapon System (SWS)
Smith & Wesson SW Model 67
Remington M40
Rock Island Arsenal M101
Rock Island Arsenal M102
Springfield M14 Rifle
Stoner M61A1 LMG
so go take a gander at all of these you might get sprayed by some noob lol