Many charges involving air weapons are brought because they are allegedly firing at above the legal power limit set down by the Firearms (Dangerous Air Weapons) Rules 1969. Power is determined by measuring the speed of a discharged pellet of known weight using an electronic chronograph, and then calculating the kinetic energy of the pellet from the resulting figures.
There is no statutory test defined to assess power, and different pellets of firing conditions can yield different results. It is therefore important to have tests conducted by the prosecution verified, and that the results are put into perspective. Pointing out, for instance, that the excess is slight, and could not be identified by someone using an air weapon may be very useful mitigation.
It should also be remembered that air weapons have existed for many years, and the exemption from the provisions of the Firearms Act 1968, given to antiques by section 58 (2) of the Act also applies to old air weapons – even high powered ones. Also, air weapons dating from before the Firearms (Dangerous Air Weapons) Rules may have been legally purchased when new, only becoming subject to legislation at a later date, again potentially allowing an opportunity for mitigation.