During 1944 the US Ordnance Department were looking at a short 30 cal. cartridge for use in a proposed light rifle. At the time there was continuous development in powder which led to standard charges for the Cal. 30 Service case (30-06 Springfield) not filling the case leading to excessive pressures. At the end of March 1944 the office of the Chief of Ordnance asked Frankford Arsenal to research the 300 Savage case loaded with Cal. 30 Service bullets. It was this experiment that ultimately lead to the 7.62×51 NATO and its adoption by the US in 1954 as well as by most major Western military forces after that.
Initial tests were done with the 165 gr. AP M2 bullet on commercial 300 Savage cases, as well as later tests during early 1945 with ordinary ball M2 bullets. The Frankford Arsenal case was designated the T65 and was similar to the 300 Savage case, but with a slightly less taper. The cases were made from standard 30-06 cases which gave a little less capacity than standard 300 Savage cases because the FA cases had slightly thicker case walls.
The dummy version was given the designation: T70 and was loaded with the M2 bullet.
Loadings with M2 ball bullet. Cases were loaded with and without primer seal. Some primers also have a ‘0’ on the primer cup that may indicate Remington primers, but that has not been confirmed.
Testing on an API round was done during late 1946 and early into 1947. The bullet was designated FAT 4 and it was similar to the Cal. 30 M14 API. The bullet weighed 117gr. with a GM jacket and knurled seating cannelure and aluminium coloured tip.
The right hand specimen was a HPT load and has a stannic stained case, with red primer sealant. These were designated T71.
As early as May 1945 the development of aluminium cases was authorised and these were designated as the T5. This contract was given to Remington.
The 30 Light Rifle cartrdiges can get very confusing, so here are 2 old threads from the IAA forum: