What he said....
except there is an odd alternative to velocity adjust....Palmers used to make a velocity adjust hammer. Basically it's a hammer that's been drilled and tapped for a small allen screw that is accessible from the slot on the drivers side where your bolt would spin out. Inside the hammer is a ball bearing. When you screw the allen screw in, it pushes the bearing back and increases velocity by increasing tension on the main spring. You might find one if you post a WTB ad....if you need pictures, I can get them to you.