I found the following reference in another US Army report. Could the EM-2 and the .280 British cartridge seen combat in the Malayan Emergency?
"The Performance of Small Arms Weapons, Including the . 280
(7 mm) Rifle, Used in the Machine Carbine Role in Malaya, "
Operational Research Unit Far East, Report No. 1/53, Mar
I searched the online DTIC database and couldn’t find it there. It might be worth it to burrow through the National Archives for this one.