I know this could be kinda old by now but just letting ya guys know.
Call of Duty: Modern Warfare 2 Update Released
January 18, 2010, 2:12 pm - Valve - Product Update
Updates to Call of Duty: Modern Warfare 2 have been released. The updates will be applied automatically when your Steam client is restarted. The major changes include:
Call of Duty: Modern Warfare 2
* Care Package, Emergency Airdrop, and Sentry Gun marker grenades sprint speed normalized
* Sentry Guns: Improved placement detection, preventing cases of Sentry Guns inside geometry
* Model 1887: Bling using Akimbo and FMJ combination now has same range and damage as non-Bling Model 1887s
* Improved player collision removing cases of getting into geometry and 'elevators'
* Mouse latency tweaks for more mouse movement consistency
* Fixes to prevent various texture and XP hacks