GYROSCOPE PLANE PLT SUSPECTS HE IS BEING SHOT AT WHEN HIS PROP WAS STRUCK BY A BOLT COMING LOOSE FROM THE STARTER.

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I WAS PERFORMING CONVENTIONAL FLT WHEN I FELT A PROP STRIKE. I CHKED FOR VEHICLE/CTL STABILITY AND BEGAN TO TURN BACK TO THE ARPT. I FELT A SECOND PROP STRIKE (OF GREATER MAGNITUDE) THAT OCCURRED MORE THAN 5 SECONDS AFTER THE INITIAL STRIKE. THE LENGTH OF TIME BTWN STRIKES CAUSED ME TO BELIEVE I WAS BEING SHOT AT BY GND FIRE. THE VEHICLE CONTINUED TO RUN SMOOTH WITH NORMAL CTL INPUTS. I QUICKLY CLBED TO 550 FT AND TRAVELED 2 1/2 MI FOR A STRAIGHT IN APCH TO RWY 36 AT MENTONE ARPT. A CURSORY EXAMINATION SUPPORTED A POSSIBLE BULLET STRIKE ON THE PROP. THE LCL SHERIFF'S OFFICE WAS INFORMED OF THE POSSIBLE ATTACK. A RPT WAS GIVEN TO THE DEPUTY. THE VEHICLE WAS GROUNDED FROM FURTHER FLT AT THE AIR SHOW. FURTHER ASSESSMENT REVEALED A LOST BOLT ON THE STARTER. THE OIL COOLER IS DENTED IN A FASHION CONSISTENT WITH THIS SIZE OF BOLT. THE PROP IS DENTED/DEFORMED CONSISTENT WITH A BOLT PROP STRIKE; OR A BULLET STRIKE. THERE DOES NOT APPEAR TO BE ANY OTHER DAMAGE/DEFECT TO THE VEHICLE. I BELIEVE I DROPPED THE BOLT THROUGH THE PUSHER PROP. I CANNOT ACCOUNT FOR THE 5 SECOND LAPSE IN STRIKES. I WILL KEEP THE VEHICLE GROUNDED UNTIL I; 1) REPLACE THE OIL COOLER; 2) RECEIVE THE PROP BACK IN AN AIRWORTHY CONDITION; 3) REPLACE/RETORQUE ALL OF THE PSRV AND STARTER BOLTS WITH A SAFETY WIRING METHOD; AND 4) NOTE MY 'FIXES' IN THE ACFT LOGBOOK. I WILL PROBABLY CONTINUE TO WORRY ABOUT INCOMING GND FIRE IF I RECEIVE 2 PROP STRIKES WITH SUCH A 'LONG' TIME BTWN HITS.