I follow CCG's & St. G's estimation as well, looking at the historical holster of the time
high riding , deep sides to encase the revolver, the reasoning to protect & secure it ( some had flaps , both military & civilian )
Pocket pistols , and some quick wrist contraptions and the Bridgeport patent may have lent to the faster to battery presentation...
Drop holsters, Buscadero's , leg ties , are the stuff of Reel History
perhaps, "quick on the trigger " was term better describing the trail weary drover ,at an Abilene or Dodge City rail head Sporting house.