I'll do my best to answer your questions. #1 AUS-Army of the United States-INF-Infantry #2 ERC-Enlisted Reserve Corp-INF-Infantry Reason for Authority for Separation-Rel to ERC SR means he was Relieved from active duty to Enlisted Reserve Corp.SR means Special Regulation He was releaved into the 5th Army Area of command.TheUS is broken down into areas.I live in NY and am in the 1st Army Area of Command.
Most sinificate Duty Assignment-Hq Co is Headquarters Company .EUSAR APO 301.APO is Army Post Office.EUSAR would be the unit he was assigned to.It is not familiar to me.
No time lost means he owed the Army no bad time, i.e.; AWOL, etc.