Re-Reading True Grit

I'm re-reading Charles Portis' classic western novel True Grit. I found a gun error by Portis toward the end of the book. It's established early on that Rooster Cogburn carries a Colt revolver in .44-40, and that his Winchester rifle is also chambered in this caliber. That would make the revolver in question most likely a Colt Frontier, which is a single-action revolver loaded via a loading gate, just as the Colt .45 Peacemaker is. Yet, in the passage where Rooster, an Indian police officer and LaBoeuf engage in a bit of impromptu target practice shooting at corn dodgers, we find this:

Rooster was holding a bottle with a little whiskey in it. He said, "You keep on thinking that." He drained off the whiskey in about three swallows and tapped the cork back in and tossed the bottle up in the air. He pulled his revolver and fired at it twice and missed. The bottle fell and rolled and Rooster shot at it two or three more times and broke it on the ground. He got out his sack of cartridges and reloaded the pistol. He said, "The Chinaman is running them cheap shells in on me again."

LaBoeuf said, "I thought maybe the sun was in your eyes. That is to say, your eye."

Rooster swung the cylinder back in his revolver and said, "Eyes, is it? I'll show you eyes!"

There ya go. You can only swing the cylinder back in on a revolver that has that feature, which the Colt Frontier didn't. The first Colt revolver to feature a swing-out cylinder was the Model 1889, and that revolver wasn't chambered in .44-40.