PLT OF A C310 FAILED TO PUT THE LNDG GEAR DOWN UPON LNDG.

Narrative

I WAS PLTING A C310Q FROM CGF TO RIC AT XA40-XB15Z AT 11500 FT MSL. MY DSCNT THROUGH 3000 FT MSL WAS UNEVENTFUL. I WAS ON A MODIFIED R BASE FOR RWY 20 AT APPROX 2000 FT MSL WHEN TWR CALLED DOWNWIND LEAR TFC FOR RWY 16. I STARTED MY PRELNDG CHKLIST WHICH CONSISTED OF RETRACT LIGHTS OUT; MIXTURES RICH; APCH FLAPS DOWN; THROTTLE BACK TO 17 INCHES; GEAR HANDLE DOWN AT 140 KTS; AND PROPS FORWARD. I INCREASED PWR TO 22 INCHES AND WAS LOOKING L FOR THE LEAR TFC. TWR TOLD THE LEAR THAT I WAS BEHIND HIM AND THAT THEY WERE CLRED TO LAND ON RWY 16. I NOW WAS LOOKING FOR THE LEAR TO MY R. LOCATING THE TFC; I WENT BACK TO THE APCH. I WAS SHORT FINAL BY NOW AND ADDED FULL FLAPS AND REDUCED PWR TO 15 INCHES. ALL SEEMED NORMAL UNTIL APPROX 5 FT AGL WHEN I EXPECTED TO FEEL RUBBER AND ASPHALT MEET. I WAS AT FULL STALL AND FULL IDLE ON THE ENGS UPON IMPACT WITH THE RWY. I BELIEVE THAT THE DISTR OF THE LEAR TFC KEPT ME OCCUPIED LONGER THAN USUAL AND I DID NOT PERFORM MY NORMAL SECOND OR THIRD GUMPS CHK SINCE I WAS AT SHORT FINAL WHEN I WENT BACK TO FLYING THE AIRPLANE. IN RETROSPECT; I BELIEVE THAT I SHOULD HAVE EITHER CALLED THE APCH OFF OR HAD THE TWR VECTOR ME CLR OF THE CONFLICTING TFC. I TEACH AND USE DISTRS ON STUDENTS REGULARLY. YET I FELL VICTIM MYSELF TO WHAT SHOULD HAVE BEEN A SIMPLE TFC CALLOUT. HAVING THE 2 RWYS COME TOGETHER LIKE A 'V' PUTS TFC XING EACH OTHER'S PATH AT THE APCH END OF THE RWY WHERE THE PLT'S CONCENTRATION SHOULD BE ON THE LNDG AND NOT ON TFC. I AM NOT SURE YET WHY THE GEAR DID NOT GO DOWN; AND I BELIEVE THAT MY MIND TOLD ME THAT IT HAD THE 3 GREEN LIGHTS. I ALSO DID NOT GET A GEAR WARNING HORN AT ANY TIME. I DID GET THE STALL HORN PRIOR TO LNDG. OWNER HAD ACFT SCHEDULED TO GO IN FOR GEAR RIGGING 4 DAYS FROM DATE OF INCIDENT. GEAR BREAKER WAS FOUND POPPED AND GEAR WAS SLIGHTLY EXTENDED UPON TOUCHDOWN. I WILL IN THE FUTURE; ALWAYS CALL OFF AN APCH IF I HAVE NOT BEEN ABLE TO PERFORM MY USUAL 2 OR 3 GUMPS CHKS.