reducing the hammer energy a bit will hardly affect (or not affect) the velocity while saving air and flattening the shot string.... My experience with regulated guns is that when the regulator creep (higher pressures when full) shows up as higher velocities, that if you reduce the hammer energy you can move the gun more towards what would be the peak of the bell-curve if it were operating non-regulated....
More hammer energy than required for a given pressure just wastes air.... It also emphasizes any velocity variation due to pressure....
