Actually, I think a Ruger Super Redhawk Alaskan in .454 Casull was used in this role. If you watch the trailer:
YouTube - Faster Official Trailer 2010 HD
until the 25 - 26 second mark and stop it, you'll see an excellent close-up of the weapon, with its distinctive Ruger hammer and cylinder release button (close-up below):
You can find out more about this weapon at Ruger's official website, here:
Ruger® Super Redhawk® Alaskan Double-Action Revolver Models
(Hover your cursor over the second model number to see the correct photo).