A semi-automatic pistol chambered in 45 ACP.
Your colt 1911a1 was made by colt in 1945.
1943 by colt
Serial number
made by colt in 1943
made by colt 1918
It was made in 1945 by Colt.
1945
In 1918
About 1943.
Proofhouse.com has Colt sn data.
made about 1917
Made in 1941.