The NSW Shooters and Fishers party has used the upcoming 20-year anniversary of the Port Arthur massacre to try and restart the debate about gun laws.

NSW upper house MP Robert Borsak says law-abiding citizens have been "unnecessarily stigmatised because of the actions of one madman" - Martin Bryant - who in 1996 slaughtered 35 people and wounded dozens.

Two weeks after Bryant's murderous rampage, then Prime Minister John Howard announced a package of gun reforms, including a ban on certain semi-automatic and self-loading rifles and shotguns.

Mr Borsak said a royal commission is needed to "allow for everybody affected by the 1996 tragedy in Port Arthur to have a chance at closure", adding that criminals, not guns, were "the problem".

"A detailed look at the event should have occurred immediately afterwards, like more recent incidents, but unfortunately it did not," he said.

"Greater than 97 per cent of all firearm-related incidents reported relate to unregistered, unbranded, unlicensed firearms."