Around 1917.
To determine the age of a 32 caliber Secret Service Special revolver with serial number 178866, you would need to consult production records specific to that firearm model and manufacturer. The Secret Service Special revolver was produced primarily in the early to mid-20th century, so the serial number can help establish a rough manufacture date. Generally, collectors and firearms experts can provide more precise dating based on the serial number and other features of the revolver.
That model was produced in 1922.
Your Colt Lawman revolver was made in the year 1972.
The Colt New Service revolver with serial number 41905 was manufactured in 1917. Colt's records indicate that the New Service model was produced from 1898 to 1944, with this particular number falling into the World War I production era. For precise details, you may want to consult Colt's official records or a reputable firearms historian.
Without a detailed description, someone would have to research every serial number of every model of revolver Colt ever made.
@ 1978
You can find out at Proofhouse.com
made about 1911
about 1918
About 1903.
Check the butt.
1923