While I think the whole moderator licensing is farce I cant see how any moderator suitable for anything bigger than a 22lr can't be classed as a firearm. The firearms act states "any accessory designed or adapted to diminish the noise or flash caused by firing the weapon" (weapon being in this instance anything producing over one joule of energy). Therefore surely any moderator designed with the structural integrity to withstand the pressure from anything above an air rifle should be classed as a firearm in it's own right?