Regional police spokesman, Johann Baumschlager, confirmed to Kronen Zeitung that police "are almost absolutely certain" the weapon found was that used by Huber, who shot and killed two policemen, a paramedic, and a member of Austria's counter terrorism special operations unit, known as Cobra, on September 17th, 2013.
Following his murderous rampage, Huber, 55, subsequently barricaded himself in a property near Melk.
Armed police and tanks surrounded the building for more than 24 hours before breaking in to discover a charred corpse in the basement.
Huber had apparently called a friend to confess his crimes as helicopters circled above the house, before ending his own life with a shot to the head.
The gun was discovered on Sunday by a former neighbour, who handed it to local police. It's thought it surfaced after the recent floods.
Experts will now examine the weapon, one of three suspected to have been used by Huber on the day of the fatal shootings.
Huber's victims had no chance of survival - so powerful is the rifle that bullets could easily penetrate a bulletproof vest. The gun is also fitted with a silencer and shell catcher, features which would have enabled the poacher to carry out his activities undetected.
According to police, since 1994 Huber had accumulated 108 fines for his illegal poaching activities, primarily in Lower Austria and Styria. Until now the total damages are calculated to be around €10 million.