NOSE GEAR RETRACTS ON TKOF ROLL. PROP DAMAGE.

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ON TKOF I APPLIED NORMAL BACK PRESSURE TO LIGHTEN NOSE WHEEL. AT APPROX 45 KIAS THE NOSE DROPPED; PITCHED DOWN. IT FELT LIKE A NOSE STRUT BOTTOMED OR A NOSE TIRE BLOWOUT. AFTER RECYCLING THE GEAR TWICE; IT OPERATED NORMAL. THERE WAS ABSOLUTELY NO VIBRATION AND ALL FLT CTLS WERE NORMAL. I FIGURED IT WAS A NOSE STRUT OR TIRE PROBLEM AND ELECTED TO CONTINUE TO MORRISTOWN; NJ; (MMU) HOME BASE. I LANDED AND TAXIED NORMALLY. UPON SHUTDOWN I OBSERVED PROP BLADES WERE NICKED ABOUT 1/2 INCH. I FEEL THE LNDG GEAR LEVER MOVED FROM DOWN TO UP WITHOUT ANYONE TOUCHING IT; POSSIBLY FROM BEING ON THE EDGE OF THE DETENT. I WOULD APPRECIATE AN AIRWORTHINESS DIRECTIVE ON SMA WITH A MORE POSITIVE GEAR DOWN LOCKING MECHANISM TO PREVENT ADDITIONAL LIKE OCCURRENCES. IF YOU HAVE ANY SIMILAR CASES ON FILE I WOULD SINCERELY APPRECIATE INFO ON SAME. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES HE IS QUITE POSITIVE THAT GEAR HANDLE WAS NOT SECURELY IN DETENT. HE WAS DEMONSTRATING TO PLT PAX HOW GEAR WORKED AS THEY WERE TURNING BASE TO FINAL. ALLOWED PLT PAX TO OPERATE THE HANDLE. 3 GREEN CAME ON BUT APPARENTLY NOT SECURELY DOWN AND LOCKED. RPTR ALSO STATED THAT ACFT HAD HAD COMPLETE NOSE STRUT FAILURE 2 DAYS PRIOR AND HE BELIEVED THIS MIGHT BE A RECURRENCE.