For 19th-century models, serial number lookup relies on exhaustive reference books like Frasca’s The '65 and '66 Springfield or Poyer’s books on Civil War rifles. These records are often less precise, providing a year of production rather than a month. A lookup on an 1873 Trapdoor might tell you it was made in 1885 and likely saw service on the Western frontier.
Usually found on the frame, above the trigger guard, or on the underside of the accessory rail. Rifles (M1A): Stamped on the rear of the receiver. serial number lookup springfield armory