Airsoft guns are replica toy guns used in airsoft sports. They are a special type of low-power smoothbore air guns designed to shoot non-metallic spherical projectiles often colloquially (but incorrectly) referred to as "BBs", which are typically made of (but not limited to) plastic or biodegradable resin materials. Airsoft gun powerplants are designed to have low muzzle energy ratings (generally less than 1.5 J, or 1.1 ft⋅lb) and the pellets have significantly less penetrative and stopping powers than conventional airguns, and are generally safe for competitive sporting and recreational purposes if proper protective gear is worn. Depending on the design mechanism for pellet propulsion, airsoft guns can be categorized into two groups: mechanical, which consists of a coil spring-loaded piston air pump that is either manually cocked (e.g. spring guns) or automatically cycled by a battery-powered electric motor gearbox (e.g. AEGs); and pneumatic, which operates by valve-controlled release of prefilled bottled gas such as compressed propane mixed with silicone oil (commonly known as "Green Gas") or CO2 canisters (e.g. GBB guns). As toy weapons, airsoft guns can often be designed to realistically resemble genuine firearms in external appearance, and it can be very difficult to visually distinguish from one despite the orange muzzle tips in some jurisdictions.