Ben Tyler's gun is identified throughout the episode as a .36 Starr. While the Star Model 1858 (the first revolver made by the company) was indeed a double-action in .36 caliber, the piece Tyler carries is a single-action Colt Model 1851, which also happens to be a .36.
When Paladin slams the door on the mayor, and the shotgun fires, it should have killed Nelson and Tyler, because it was pointing directly at them while they stood about 12 feet away, yet they are unharmed.
Ben is shown in credits as "Ben Tyler", but called Bert twice. That name appears in newspaper article as well.