After the M14's adoption, Springfield Armory began tooling a new production line in 1958, delivering the first service rifles to the U.S. Army in July 1959. However, long production delays resulted in the 101st Airborne Division being the only unit in the Army fully equipped with the M14 by the end of 1961. The Fleet Marine Force finally completed the change from M1 to M14 in late 1962. Springfield Armory records reflect that M14 manufacture ended as TRW, fulfilling its second contract, delivered its final production increment in Fiscal Year 1965 (1 July '64 – 30 June '65).
The M14 remained the primary infantry rifle in Vietnam until it was replaced by the M16 in 1966–1967, though combat engineer units kept them several years longer. Further procurement of the M14 was abruptly halted in late 1963 due to the above-mentioned Department of Defense report which had also stated that the AR-15 (soon to be M16) was superior to the M14. After the report, a series of tests and reports by the U.S. Department of the Army followed that resulted in the decision to cancel the M14. The M16 was then ordered as a replacement for the M14 by direction of Secretary of Defense Robert McNamara in 1964, over the objection of those Army officers who had backed the M14 (other factions within the Army research and development community had opposed the M14 and the 7.62×51mm round from the start). Though production of the M14 was officially discontinued, some disgruntled troops managed to hang on to them while deriding the early model M16 as a frail and under-powered "Mattel toy" that was prone to jam. In late 1967, the U.S. Army designated the M16 as the "Standard A" rifle, and the M14 became a "Limited Standard" weapon. The M14 rifle remained the standard rifle for U.S. Army Basic Training and troops stationed in Europe until 1970.