A masked gunman tried to shoot an elderly couple outside a staff Christmas party, pulling the trigger at least twice before realising the gun had malfunctioned and had not discharged.

Brian and Otwina left the Christmas party in Melbourne's west on December 19 last year and were chatting in the car park outside about 1am when a balaclava-clad man emerged from behind a dumpster and pointed a large gun directly at them.

He demanded they open the door to the party venue on Talmage Street in Sunshine.

But the couple refused and Brian, 79, tried to wrestle the gun from the man, with the struggle was captured on CCTV cameras.