The Colt New Service revolver was introduced in the early years of the 1900's as a large frame revolver chambered in many rimmed calibers, including .44
special, .38-40, .44-40, .45 Colt, .455 webley, etc. Later calibers included .38 special and .45 ACP. It was made up to 1940 and production did not resume after WWII.
The Colt M1917 was only made during 1917-1918 to fulfill a US Military requirement for a .45 ACP revolver due to a shortage of M1911 pistols. S&W came up with the idea of using half-moon clips for loading, firing, and extracting the rimless .45 ACP cartridge in a revolver. Both companies produced about 150,000 revolvers each, with a utilitarian brushed or dull blue finish. The pre and post WWI revolvers had higher polish Colt bluing. The earliest production of several thousand guns had bored thru chambers, and could only be fired using half-moon clips. All later Colt production, and all S&W production used the stepped .45 ACP chamber which allowed firing without half-moon clips.
To be properly called a M1917, the revolver has to be chambered for .45 ACP, carry US Property markings on the barrel, be fitted with a lanyard loop, and have a serial number within the range of New Service models. Various Government markings on the butt and frame also apply. If your gun is missing some or all of these features, it is a civilian New Service revolver.
HTH
John