By the serial number. Go to proofhouse .com
The Colt 1911 was designed in 1897 and adopted by the US Army in 1911.
made 1917
Your Colt model of 1911 dates to the year 1918,with the serial number that you have supplied.
1944 & 1945
A Colt 1911 commercial .45 with that serial number was made about 1971
A Colt government model with that serial number was made in 1918.
Colt 1911 .45 serial # 171885 was manufactured in 1917.
Colt Firearms ((named for its founder, Samuel Colt) was one of the firms that made the US Military Pistol, Cal .45 ACP, Model 1911. It was adopted by the US Government in the year 1911.
It was made in 1918.
1950-1951
Call Colt
Good pistol