What was found
AFTER NORMAL TAKEOFF AT APPROX 50 FT IN THE AIR AND PRIOR TO GEAR RETRACTION. A VERY LOUD BANG WAS HEARD WITH AN ACCOMPANYING SHUTTER. CREW CONTINUED TO CLIMB OUT LEAVING GEAR DOWN. AN EMERGENCY WAS DECLARED WITH THE TOWER, SUBSEQUENTLY A NORMAL LANDING WAS MADE.ENGINE BORESCOPED WITH NO FINDINGS, OIL SAMPLE TAKEN, OIL DRAINED, REPLENISHED AND FILTERS CHECKED WITH METAL CONTAMINATION. ENGINE RUN, OIL SAMPLE TAKEN WITH OIL SHOWING SOME BLACKNESS IN COLOR AND FILTERS SHOW METAL. OIL DRAINED AGAIN, REPLENISHED AND ENGINE RUN A SECOND TIME. OIL SAMPLE TAKEN WITH OIL STILL SHOWING BLACKNESS, FILTER STILL SHOWING METAL. ENGINE BEING REMOVED TO BE SENT TO SHOP FOR DETERMINATION OF PROBLEM AT THIS TIME.