Your friend should "right shoulder arms" the weapon, and march directly to the nearest gunsmith shop. A long time ago, I spent some time in the Army. During this period I must have torn down and cleaned at least a million M1s (seems like that many) and never seen one with a loose barrel. Matter of fact, I have seen many guns with the barrel welded in place.
I WOULDN'T FIRE THE GUN UNTIL IT WAS CHECKED, AND AN OK GIVEN BY A COMPETENT GUNSMITH.