Reward of $500K to solve bikie club murder

After more than 20 years of "indescribable pain", the mother of a man shot dead in a NSW bikie clubhouse is hoping his killer will finally be brought to justice.

The $100,000 reward has been increased to $500,000 to help solve the killing of Paul Summers at the Gosford Chapter clubhouse of the Rebels outlaw motorcycle gang on the Central Coast.

The 31-year-old was was asleep on a lounge in the clubhouse in the early hours of September 22, 1999, when bullets sprayed the front of the property.

An inquest in 2001 found Mr Summers had been fatally shot by an unknown person or persons.

His mother, Robyn Shelley, hopes the increased reward will help investigators to finally provide justice for her son.

"Paul was a much-loved son and brother and an extremely talented musician, who was planning to pursue his dream of starting a full-time music career when his life was cut short," she said on Tuesday.

"After more than 20 years of indescribable pain, we are hoping that someone will come forward and help identify those responsible for Paul's death."

Homicide Squad Commander, Detective Superintendent Danny Doherty, said there were people who were there on that night and know what happened.

"Investigations since 1999 have been hampered by the nature and location of the incident being linked to the outlaw motorcycle gang network," he said.

"We know there are people who haven't provided police with the whole story. Now, after more than 20 years, it is time for those individuals to come forward," he said.