Well i would show you how to do both but unfortunately im only on xbox. Some tips for no scopes:
1. Use the G-shot, Which is basically strafing in a direction, stopping so the crosshairs go small again then shoot and strafe in the opposite direction.
2. Switch weapon technique, which is where you tap Y ( or triangle for ps3 users) which will cause the weapon to switch but just before it changes weapon tap Y or triangle again at the same time as the fire trigger. This is quite accurate at long distance shots.
3 pop shot, this seems to be quite accurate on mw2 and basically you tap both the aim and fire trigger at the same time.
I have some cod 4 montages on youtube where i use these techniques, but obviously thats cod 4 and not mw2 but the aspect stays the same with the techniques.
Hope this helps.