Willin' to bet it started with a 7 1/2" barrel also.If this gun was made in 1879, it has had the bbl replaced because the caliber was not stamped on the bbl, it was on the trigger guard, the ejector rod head should be a "doughnut" style instead of a "half moon" style. The hammer is a correct "pre war" hammer, but hard to tell from the pictures if it is correct for 1879. The grips are not original as it would have had one piece walnut grips. It appears to have been heavily buffed before engraving and plating, the engraving is not "factory" style, so I'm pretty sure it was engraved after leaving the factory.
Still, a nice old Colt and a pleasure to own!