What is Airsoft? The term "Airsoft" (sometimes referred to as SoftAir) has two common use meanings:
1. Models: Airsoft replicas are non-lethal "look-a-like" models of real life firearms. These toys project inert round plastic balls (referred to as BBs) at safe speeds. Airsoft models typically have muzzle energies of 0.2-0.8 Joule and are non-lethal. Airsoft models use 6mm BBs as consumables, however 8mm BBs are available but less popular.
2. Game/sport: Airsoft is also commonly used to describe a team based wargame/battle simulation game played using the models described in (1). The game is played in a series of game scenarios run in a similar style to those in paintball with opposing teams competing against each other. A player is considered "hit" and therefore out of play when a BB touches them when projected from an opponents Airsoft model. The winning team is normally either the one with players still in play, or the one which achieves the scenario's goal first.
1 Joule? Under United Kingdom (UK) law Airsoft models are non-lethal, anything that is considered lethal (i.e. over 1 Joule) is under UK law not "Airsoft". A replica or model from an Airsoft manufacturer over 1 Joule would be considered a lethal barrelled weapon from which a shot could be discharged, and therefore a Firearm - most likely to be classified as an Airgun.
Two classifications of model are available from the mainstream Japanese manufacturers, one is marked ASGK, the other JASG. Unmodified ASGK models should all be below 1 Joule in muzzle energy and should therefore be suitable for gaming use at any site in the UK. JASG models are more than likely over 1 Joule in energy and in the UK suitable for target use only - other countries may have different rules. Whilst this is not a definitive rule, it can be helpful in some circumstances.
Whilst low powered Airweapons may be legal to own, under certain restrictions, anything over 1 Joule in muzzle energy is unsuitable for use in a gaming environment in the UK.
Please remember that international laws differ from UK law.