The standard rule for rapid fire is -2 OCV per additional shot and 1/2 DCV. The first missed attack causes all following attacks to miss.
Not only is there little valid real life reason to assume that one's second shot is doomed to failure because your first was off target, but the result is counter-genre in many cases. The restriction is removed. Also counter-genre is the huge DCV effect, the 1/2 DCV modifier is also removed.
In compensation for lifting these restrictions, the OCV modifier is increased to -3 per additional shot.
Rapid Fire is a full phase action.
An alternative to the simple rapid fire of blazing guns, is the superheroic attack of bouncing a attack off one or more foes with a single strike.
This attack is considered a special case of Rapid Fire and takes the normal modifiers as detailed above. In addition a skill level must be assigned to each 'bounce' that the attack makes as normal for the bouncing rules (see page 377 of the Main 5th edition rulebook revised).