What was found
COMPLETED A FLIGHT AND WHILE OPENING THE MAIN CABIN DOOR NOTICED HANDLE WAS LIGHLY STIFF & THEN LIGHTLY POPPED UP AND WAS WORKING. THOUGHT IT WAS PERHAPS "USER ERROR". WE THEN VERIFIED BY OPENING AND CLOSING THE DOOR A FEW TIMES TO SEE IF IT COULD BE DUPLICATED. NO ISSUES WERE NOTICED. AFTER A SECOND FLIGHT AT FLIGHT LEVEL 430 FOR OVER THREE HOURS, I ATTEMPTED TO OPEN THE MAIN CABIN DOOR. THE HANDLE WAS VERY STIFF WITH A SIGNIFICANT BIND AND THEN SUDDENLY BROKE FREE WITH A VERY LOUD BANG. THE DOOR FUNCTIONED NORMALLY DURING THE REST OF THE CYCLE. CLOSED AND OPENED THE DOOR A FEW TIMES AND HAD NO OTHER ISSUES CORRECTIVE ACTION: LOCK HOOK ADJUSTED. OPS CHECK COMPLETE. IAW CL-350 AMM 52-11-05-05.