Copper failed to extend gains into a third day Friday, ending lower, as further tightening moves in China, Middle East unrest and Japan's nuclear crisis kept investor risk at a minimum. COMEX copper for May delivery eased 0.50 cent to settle at $4.3390 per lb in lighter-than-usual volume. According to Thomson Reuters preliminary data, COMEX volume traded stood just above 30,100 lots, over 40 percent below the 30-day norm.