The left side of the slide contains the primary manufacturer identification, which changed over time.
There are several types of markings that can be found on a Remington Rand 1911A1, including: remington rand 1911a1 markings
(early production), which helps distinguish them from Colt ("No."). M1911A1 U.S. ARMY: Stamped on the right side toward the front of the frame. Inspector Mark: The left side of the slide contains the