This is an outstanding example of an experimental (preproduction set-up examples) Union Switch & Signal 1911A1 pistol. A number of receivers and slides were manufactured prior to full production to set up and test the machinery. Approximately 100 pistols were later assembled from these preproduction parts, with most reportedly being presented to officers and employees of the company. They all bear the special preproduction experimental serial numbers "EXP No" followed by 1 through 100. These pistols are known to show a variety of finishes with this example exhibiting the blue over sandblasted finish which gives the appearance of a deep black parkerization. A similar example, serial number EXP No 21, is pictured on p. 326 of Clawson's "Colt .45 Service Pistols Models of 1911 and 1911A1". This example is marked on the left of the slide with the standard "USS" logo followed by the Swissvale address on the left of the slide and "US&S CO/EXP No 44" on the right of the frame, with no other markings visible. It is fitted with the standard blade and notch sights, thin checkered hammer, short stamped trigger, long grip safety, arched checkered mainspring housing, reinforced Keyes Fiber grips, and a "B" marked two-tone magazine.