Very puzzling problem in Call Of Duty

Hi guys..
I have played COD since almost the beginning..but 2-3 months ago noticed something that surprised me alot. I had always thought that EVERYONE had the same image shake...meaning the movement of your screen(image) when you are shooting an MG.

After watching any number of players..it finally dawned on me that there are SOME guys who have little or no image shake from the recoil effect. I usually have a good deal of this recoil effect..or image shake. Mostly it causes the image in front of me to go UP AND DOWN!! That includes players..buildings..everything. Some guys though...have a very smooth image(screen) when they are shooting. I have mostly thought it was a hack of some kind...but I have never heard of such a hack. If you dont exactly understand what I'm saying..take a MG(say a Tommy.or mp40) and face toward some buildings..it doesn't need to be a close up. Start shooting and watch your screen. DO NOT...I repeat do not watch the gun barrel. IT always moves..or it should(grin). If there is a shaking of the image in front of you(direction you're shooting) then I believe that is NORMAL. Why do some players not have this?. Do any of you here know the answer to that? I do know it is NOT the video card or the speed of ones connection. Thanks for any response. I do really appreciate it. Have a good one

Fighting Falcon