OTTAWA -- The Liberal government is expected to announce this week an ambitious program to buy back legally owned firearms that it last year deemed to be assault rifles.

Legislation implementing the buy-back program would make good on a commitment the government made in May in response to the mass shooting in Portapique, N.S., that left 22 people and the gunman dead.

After the shooting, the government reclassified as 鈥減rohibited鈥� about 1,500 different firearm models and their variants, including the AR-15 rifle that was used in many mass killings in the U.S., and the Ruger Mini 14, a hunting rifle used in the Ecole Polytechnique massacre in Montreal in 1989.

Rifles like the AR-15 that had been classified as 鈥渞estricted鈥� previously could only be used legally on shooting ranges. But now that they are prohibited, they can still be legally owned by those with a prohibited class licence but cannot be used, making them useful only as collectors items.

The legislation is expected to detail how owners of these firearms can surrender them to police and obtain financial compensation. The rates of compensation the government will pay for each rifle is expected to be listed in regulations that will accompany the bill.

Owners of prohibited rifles will still have the option to hang on to them subject to strict conditions on storage -- a point that has riled gun-control advocates who want to see mandatory confiscation of firearms they believe to be military in nature.

Firearms advocates have argued that the reclassification was too broad and focused on the appearance and not the function of many semi-automatic rifles the government deemed to be military in nature.

The Canadian Coalition for Firearms Rights and other applicants to obtain an injunction blocking the reclassification. The request for the injunction was dismissed earlier this month. 

The Liberals are following the lead of Australia, which launched of many semi-automatic guns after a mass shooting in 1996 in Port Arthur, Tasmania.

The Australian buy-back cost the government an estimated AUS$304 million, plus another $61 million in administration and advertising costs, and reduced the number of firearms legally owned by individuals by about 640,000.

Although there is conflicting research on the effect of the program, the number of gun-related deaths, both homicides and suicides, fell in

By making the buy-back voluntary, the Liberals hope to avoid the political damage the party suffered from the introduction of the so-called long-gun registry, which required owners of all classes of firearms to register them in a database maintained by the RCMP.

The requirement to register non-restricted shotguns and rifles proved especially unpopular with many gun owners in rural and Western Canada. Stephen Harper鈥檚 Conservative government eventually scrapped the requirement and ordered those records purged from the database.

The RCMP, however, still maintains a database of registered restricted-class and prohibited class firearms, which will likely be used to publicize the buy-back program.

The government gave notice last week that it intends to table the implementation bill, which could come before the House of Commons this week. The bill is also expected to include new measures to curb illegal trafficking and cross-border smuggling of guns.