The Colt M1911 served as the standard issue firearm of the U.S. Army from March 13, 1911, until Jan. 14, 1985. The model that went into service in 1911 remained unchanged for 13 years until 1924 when the gun underwent minor changes. The modifications were considered improvements, however minor, and the modified version of the Colt was designated the Colt M1911A1. Being able to identify an original model Colt M1911 therefore comes down to being able to differentiate it from a Model 1911A1.
Items you will need
M1911 photo reference
M1911A1 photo reference
Examine the double-diamond reliefs on the top and bottom of the checkered handle grip. The original M1911 has diamond shapes while the M1911A1 has small circular shapes. This alone can distinguish the M1911 from the similar M1911A1.
Compare the triggers. The original M191 has a longer trigger, meaning that the trigger curve extends farther than the shorter trigger on the M1911A1.
Compare the hammer spurs. It's a minor difference, but the original M1911 has a slightly longer spur on the hammer than the M1911A1.
Examine the grip safety spur. The original M1911 will have a grip safety spur that juts out less than the grip safety spur of the M1911A1.
Compare the front sights. This can be difficult without direct comparison, but the original M1911 will have a slightly more narrow front sight than the M1911A1.