See the airgun article for information on how spring piston and pneumatic airguns work. Cyprus also controls airguns, and airgun owners require a license. An airgun slug is a new type of pellet recently developed for pre-charged pneumatic airguns. These are generally fired with rimfires or airguns. Suppressors for all firearms, including airguns, are prohibited in Canada. It is also commonly used as a propellant for airsoft airguns. Crosman has manufactured and sold the Benjamin-Sheridan and Sheridan model airguns for many years. Piston airguns, often called "springers", are unique in many ways. "Specially dangerous airguns" require a firearms licence for possession and use. Competitions are also held with airguns and black-powder firearms. Airguns up to 17 Joules of muzzle energy are unregulated. Most BB-firing airguns can shoot faster than . Commercial sales of airguns may only take place in licensed gunshops. Axelsson developed with a three-stage hand pump that alleviated this difficulty of refilling PCP airguns. Sound sources used include airguns, vibroseis and explosives.