"Most of the legend of the M14 seems to be based on National Match, M21, and other custom-tuned examples. Ironically, during its brief production run, the rack-grade M14 was considered to be inferior to the earlier M1 Garand in both design and workmanship. In March of 1962, Aberdeen's Development and Proof Services released "Report on Tests for Ad Hoc Committee on Accuracy and Testing of 7.62mm Ammunition and M14 Rifles". For the testing, twenty-one M14 rifles had been chosen at random from rifles already accepted for military issue. Three manufacturers (Springfield, Winchester, and H&R) were represented by seven new rifles apiece.
* All of the rifles from Winchester and H&R exhibited excessive headspace.
* All of the rifles had loose handguards.
* 95% of the rifles had loose stock bands.
* 90% of the rifles had loose gas cylinders.
* 75% of the rifles had misaligned op rods and gas pistons.
* 50% of the rifles had loose op rod guides.
* 50% of the rifles had op rods which rubbed the stock.
* Three rifles had barrels which exceeded the maximum bore dimensions.
* Only three rifles had an average bore diameter which fell below the accepted mean diameter.
* One rifle was found to have a broken safety while another had a misassembled safety spring.
* One rifle had a misassembled flash suppressor which was actually contacting bullets during live fire tests
A barrel from each manufacturer was sectioned for examination of the bore and chrome lining. The chrome lining was out of tolerance (uneven and on average too thin) in all three barrels. The H&R barrel also failed the surface-finish requirements.
During accuracy testing, the M14 rifles produced greater group dispersion and variation in the center of impact than the control rifles (two M1 Garands rechambered for 7.62x51mm along with two AR10). NATO testing was quoted indicating that the Canadian C1 (FN FAL) and German G3 were also less sensitive to variations within and among ammo lots.
Shutting off the gas port in the M14 rifles resulted in an average 20% reduction in extreme spread compared to those groups fired with the gas port open. This also reduced the variation in the center of impact. "