Aiming feels very clunky for me, is mouse acceleration on by default? If so, how do I fix it?

I make a movement that should move the crosshair from the shoulder to the head but it barely moves.

Mouse feels fine to me. Though if I crank up all graphics settings I get a mouselag accompanied by heavy framedrops, especially if I turn on mirror, SSAO to higher then normal, FXAA to 2x or 4x and physx to ultra. On default settings I get decent framerates (never below 30FPS) and a lag free experience.
So, what are your hardware specs?

My System:
Win7 Pro 64Bit
Phenom II X4 965 @ 4.0 Ghz
6GB DDR2 1066 RAM
Geforce GTX 660 TI

It might also be lack of accuracy upgrade. And the pistol sucks.

Check your weapon inertia value in options 'game' menu I believe. I set it high to start because I wanted the Katana to feel like a real sword when swinging sadly it was still shit and my guns were lagging because of it.

This fixed it! Thank you so much!

Yeah it's almost a bug the way it transfers across both long heavy weapons (the sword) to what would be more heavily influenced by recoil (the subs). could have been a nice feature if a)it didn't and b) there was a instanced inverted mouselook button.
Oh and has anyone been missing the doom/wolfenstien era strafing? I did *sniffles

So what is a good middle road setting for inertia?