You could try turning it off in windows (increase mouse precision).
I always have that off. It seems like it's integrated in the game's engine by default and It's kinda hard for me to get used to aiming with mouse acceleration when I always use raw-input in all of my games so just that has put me off playing the game. Weird thing is, I once played combat arms for some time and if I remember correctly, it didn't have mouse acceleration back then. For a game trying to be more competitive that's a pretty stupid thing to add.