Picard examines a 500 year old Colt .45
The Colt .45 was a projectile weapon popular in the 19th and 20th centuries. The .45 single action cavalry pistol was invented by Colt Firearms in 1873.
In 1893, Samuel Clemens owned a Colt .45 which was lost to time under San Francisco, only to be later discovered in the 24th century. (TNG: "Time's Arrow", "Time's Arrow, Part II")
Background
Data incorrectly refers to the Colt revolver discovered at the archeology site as a ".45 caliber double action cavalry pistol invented by Colt Firearms in 1873.". In actuality, Colt never produced a double action revolver in 1873. The revolver was in fact a "Colt Single Action Army" also known as "The Colt Peacemaker" (see external links below).