.455_hunter:
That serial number should date to 1960. As such the gun should have a model number stamped under the cylinder yoke. The model should be 10 if a steel frame, 12 if Aluminum.
android:
You have a .45 Hand Ejector US Army Model of 1917, with the frame manufactured between Sept. 17 1917 & January 1919.
If you read back a couple of pages in this thread you will find DrakeGmbH's excellent photographs of his 1917 which appears to have been factory reworked and sold as new in the 1950s. These will show you where to look for military markings.
The grips on your gun are correct for a commercial sale prior to 1938, but it lacks the S&W logo on the left side of the frame that guns manufactured for civilian sale are supposed to have.
S&W bought back a large number of parts and frames (read guns) from the US Army at the end of WWII and assembled them as new guns. So although originally manufactured in 1919, your gun may have been re-manufactured in the 1950s. It may also have been an overrun gun sold commercially at the end of WWI, or one that had been 'liberated' by a soldier.
Regardless, the caliber is .45 ACP and it is designed to be loaded with half moon clips, or if you can't find them, look for .45 Auto rim, which is the .45 ACP with a rim to allow chambering in these revolvers.