During World War 2, Springfield Amory in Springfield, Mass. developed the T20-series of rifles. This rifle was a selective fire design that was modified to accept the BAR 20-round magazine. Various compensators and muzzle breaks were tired along with a modified gas system. The last models of the T20 used the roller locking lug found on the T44E4 rifle, type standardized as the M14 in 1957.
The T20 rifle pioneered the selective fire design later applied to the T44 (M14) rifle. If the war in the Pacific would have continued into 1946, the T20 rifle would have probably been put into production due to the additional firepower it would have given the individual infantry soldier. As it was, the T20-series still had bugs that continued past the end of the war and the project was shelved until the Army decided on the 'Lightweight Rifle Project.'
The LWP was an attempt to design a rifle in the weight range of the M1 carbine that fired a cartridge equivalent to the .30-06 from a 20-round magazine, and deliver either semi-automatic or full-automatic fire. During the LWP design phase, the .30 caliber cartridge was downsized to the T65E3 (7.62x51 mm NATO) and three separate rifles were designed to fire it: T25, T47, and T44. The T44 was a product improved T20 (which was a redesigned M1).
The T25 and T47 designs were dropped in favor of the T44. By that time, the T44 was in competion with the FN FAL design called the T48. In a continued series of head-to-head trials with the FN designed T48 rifle, the T44E4 tied with the T48. Assured by Springfield Armory that the T44 could be more cheaply manufactured using existing M1 production machinery, the Secretary of the Army type standardized the T44 as the M14 rifle in 1957. It was later found out that Springfield had to replace its M1 tooling to produce the M14, but that was after the decision had been made.
In a curious quirk of fate, the last design done by John C. Garand before he retired from Sprinfield Armory was the 20-round magazine for the T44 (M14) rifle. Mr. Garand designed a simple box magazine that had the lowest stripping force for 7.62 NATO rounds of all contemporary magazines chambered for this caliber (FN FAL and Commonwealth, G3, CETME, BM59, AR-10 rifles).