Detectives hope the information will jog memories about the murder of Alistair Wilson, 30, from Nairn in the north of Scotland.
The father-of-two was gunned down at his home on Sunday November 28, 2004, sparking a major manhunt.
Although the make and type of gun was quickly revealed, officers have narrowed down its possible age. The gun is a Haenel Suhl Model 1 Schmeisser patent handgun, manufactured between 1920 and 1945 at a factory in Germany, Police Scotland said.
The ammunition is .25 calibre made by Sellier and Bellot between 1983 and 1993 in what is now the Czech Republic.
Council workers found the small gun on December 8, 2004 in a drain on Seabank Road in the coastal town, 16 miles east of Inverness.
Detective Superintendent Malcolm Stewart said: "Alistair's loved ones are still grieving for his loss and they deserve answers. They deserve justice. We cannot lose sight of that and we are determined to get it for them.
"The passage of time can lead to significant changes in people's associations. Those who may have been reluctant to come forward with information nine years ago, for whatever reason, may be more willing to do so now."
Mr Wilson was with his family on the evening of his murder. The doorbell rang and his wife, Veronica Wilson, went to the door and saw a stocky man wearing a baseball cap and holding an envelope.
He asked for Mr Wilson, who went to the door and was then shot. Mr Wilson was taken to Raigmore Hospital in Inverness but was later pronounced dead.