What does venting do?
The gas travels faster than the ball, thus knocking it off course when the ball exits the tip. Venting dissipates that blast behind the ball creating a less turbulent cylinder of gas. This helps keep the ball on course and reduces the report. Dual venting is a little quieter but is a less efficient than the single.
Standard venting service is 2 spirals 3 inches long. This is a service to port your existing barrel.