what your'e talking about is direclty underneath the barrel and faces teh same dicrtion as the barrel, correct? that's your low pressure regulator. It regulates the pressure that goes to your soleniond
How about a litte more info like make and model of the marker. Are you talking about the front of the reg or in the area of the reg. For instance on my Invert the front of the reg has an adjustment screw that adjusts the pressure to the marker but not for adjusting your velocity.