The type of gun used in the fatal school shootings in Newtown, Conn., can be legally purchased in Canada but with modifications to comply with this country's laws.

Police said that the gunman used a Bushmaster AR-15 semi-automatic rifle in the shootings that killed 20 children and six staff members at Sandy Hook Elementary School on Friday.

While the weapon can be purchased in Canada, there are significant differences between the Canadian and U.S. versions.

Gordon McGowan from MilArm Co. in Edmonton said federal law requires magazines to be altered to take no more than five cartridges, which limits the number of shots before reloading.

"Physically, the magazine itself is generally the limiting capacity," McGowan said.

"In this particular instance, this is a 30-round magazine that's been altered to accept no more than five cartridges. So in the U.S. marketplace, yes, this would be a 30-round magazine."

McGowan said the Canadian version of the gun has also been changed to make it difficult, if not impossible, to turn them into fully automatic weapons.

"A semi-automatic-only trigger mechanism, one depression of the trigger, equals one cartridge fired," he said.

Canadian gun laws also place restrictions on ownership. Owners must have the appropriate licenses, take a safety course and pass background checks. It also takes up to 60 days to purchase a weapon.

Semi-automatic rifles like the Bushmaster AR-15 can only be used legally at approved shooting facilities

With files from the CBC's Scott Fralick