On pages 169/170 of the current paper back version of 'True Grit', Mattie comments:
"He got out his sack of cartridges and reloaded the pistol. Rooster swung the cylinder back in his revolver and said ...... "
This was during the shooting contest between Cogburn and LaBoeuf when they were aerial shooting 'corn dodgers'.
Granted that Mattie was unfamiliar with handguns other than her father's Colt Dragoon, but this implies that perhaps Cogburn was shooting a Colt 1878 DA.
It is possible that Mattie could have thought the act of closing the loading gate was 'closing the cylinder', but ......