Early in the story, Matt makes a remark to Tom to the effect that he is one of the few men in the area who still carries a .36 caliber Colt Navy revolver. That might have been true for the fictional Dodge City, but in the actual West, Colt Navy revolvers - the most popular revolving pistols of the 1850's and 1860's - were common in the 1870's and into the 1880's, many converted from their original percussion ("cap & ball") configuration to use metallic cartridges. The "Navy" part of the name did not refer to that sea service, but to a decoration on the cylinder depicting a naval battle in the Texas War of Independence.