AN EIGHTH BOMBER STATION, Sept. 27 -- Ordnance experts here were studying today one of the largest pieces of flak yet known to have struck an American bomber at operational altitude -- a 12-pound chunk of steel eight inches wide and almost three feet long.
    The flak fragment imbedded itself in the upper side of the B17 Skin and Bones' left wing just as the bomber, piloted by 1/Lt. Franklin Berry, of Poughkeepsie, N.Y., left the target area over Emden.
    Ordnance men said that from a preliminary examination of the flak it probably came from a shell or rocket weighing at least 125 pounds.