The M100 is a blowback

Blowback (arms)

Blowback is a system of operation for self-loading firearms that obtains energy from the motion of the cartridge case as it is pushed to the rear by expanding gases created by the ignition of the propellant charge....

-operated semi-automatic

Semi-automatic firearm

A semi-automatic, or self-loading firearm is a weapon which performs all steps necessary to prepare the weapon to fire again after firing—assuming cartridges remain in the weapon's feed device or magazine...

 rifle chambered in .22 LR or 9x19mm Parabellum, manufactured by Calico Light Weapons Systems

Calico Light Weapons Systems

Calico Light Weapons Inc. is a privately held firearms manufacturing company based in Cornelius, Oregon. The company was established in 1982 in Bakersfield, California, and released its first production weapon in 1985. Calico was sold in 1990 but remained in Bakersfield...

 in Hillsboro, Oregon

Hillsboro, Oregon

Hillsboro is the fifth-largest city in the U.S. state of Oregon and is the county seat of Washington County. Lying in the Tualatin Valley on the west side of the Portland metropolitan area, the city is home to many high-technology companies, such as Intel, that compose what has become known as the...

, USA and possessing a unique 100-round helical-fed magazine mounted on top of the weapon. The introduction of the Federal assault weapons ban

Federal assault weapons ban

The Federal Assault Weapons Ban was a subtitle of the Violent Crime Control and Law Enforcement Act of 1994, a federal law in the United States that included a prohibition on the manufacture for civilian use of certain semi-automatic firearms, so called "assault weapons"...

made manufacture of the Calico family of weapons for sale to civilians illegal because of the high magazine capacity until the legislation expired. The company is now allowed to build the exotic firearms in their original configuration.