The OP needs to add the word "New" to Colt "Service"revolver.

The model is properly the Colt New Service. Read the boxes!

Charles Askins had the USBP adopt the New Service .38 in the late 1930's. I asked him why he didn't just adopt the S&W .38-44 for its front cylinder lock and better action. The S&W also retains its cylinder timing longer.

He said that he just liked the Colt factory reps better. The S&W reps were rude amd arrogant.

He had to turn the barrels on almost all of those Colts to get them sighted-in.