any device (commonly known as a bump stock) which is designed or adapted so that—
(i) it is capable of forming part of or being added to a self-loading lethal barrelled weapon (as defined in section 57(1B) and (2A)), and
(ii) if it forms part of or is added to such a weapon, it increases the rate of fire of the weapon by using the recoil from the weapon to generate repeated pressure on the trigger