A C421 PLT UNABLE TO LOWER THE R MAIN GEAR; LANDED ON THE L MAIN AND NOSE GEAR. NO PAX OR CREW INJURIES DURING EMER LNDG. NO FIRE.

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I WAS CAPT ON A PART 135 FLT FROM ZZZ1 TO ZZZ2; VMC BUT FILED IFR. ARPT IN SIGHT; CANCELED IFR; ENTERED L DOWNWIND RWY 25. SLOWED ACFT TO 125 KIAS; APCH FLAPS; PUT GEAR LEVER 'DOWN' ONLY L MAIN GREEN LIGHT. RECYCLED; L MAIN AND NOSE GREEN LIGHT. NO R MAIN LIGHT. PERFORMED CHKLIST ITEMS; DID FLY-BY. GND PERSONNEL SAID L MAIN AND NOSE GEAR DOWN; APPARENTLY LOCKED; R MAIN UP IN WING. AFTER SEVERAL ATTEMPTS TO RECYCLE GEAR; I USED THE EMER GEAR PROC (BLOW-DOWN BOTTLE). STILL NO R MAIN DOWN INDICATION. AFTER 2 MORE FLY-BYS FOLLOWING CONTINUED MANEUVERS TO TRY AND GET R MAIN; I DEPARTED TO ZZZ3 WHERE THERE WAS A MAINT FACILITY. I CONTACTED TWR AT ZZZ3; THEY APPROVED A NUMBER OF CIRCUITS N OF THE ARPT IN FURTHER ATTEMPTS TO EXTEND GEAR. NONE WERE SUCCESSFUL. I WAS GETTING DOWN TO 45 MINS ON FUEL. AFTER ANOTHER 15 MINS; FUEL WAS TO THE POINT WHERE I DID NOT WANT TO KEEP TRYING TO GET GEAR DOWN AND ATC CTL TWR CLRED ME FOR FLY-BY; CONFIRMED R MAIN STILL IN WING. I SELECTED GEAR LEVER 'UP' TO LAND FLAT WITH BOTTOM ON RWY. ON FINAL; BOTH TWR AND ACFT ON GND TOLD ME L MAIN AND NOSE GEAR WERE STILL DOWN. I WENT AROUND AND SET UP FOR LNDG AS CONFIGURED. THE LNDG WAS SUCCESSFUL; MIXTURES AND FUEL VALVES CLOSED; ALL SWITCHES OFF AND PAX SAFELY EXITED AIRPLANE. ARPT EMER PERSONNEL SPRAYED FIRE RETARDANT BUT AT NO TIME WAS THERE ANY SIGN OF FIRE OR DANGER OF FIRE. THE PROB HERE SEEMED TO BE ENTIRELY MECHANICAL AND ALL APPROPRIATE PROCS AND CHKLISTS WERE ACCOMPLISHED. AT NO TIME DID THE ACFT EXIT THE RWY. TWR CTLR WAS EXTREMELY HELPFUL AND PROFESSIONAL AS WERE THE EMER CREW WHO MET THE ACFT ON THE RWY. THERE WERE NO INJURIES OF ANY KIND TO PAX OR MYSELF.