My hammer in the .25 Disco, when the face is recessed far enough, has a "solid hammer stop" consisting of an energy absorbing elastomer on the back of the valve.... The valve lift at 3000 psi is about 0.095", and as soon as you recess the hammer face far enough that the stem is only opened physically that far (assuming constant contact with the hammer), the velocity starts to drop.... Take a look at this graph....



I measured the lift (dotted lines, right hand scale) by using an O-ring on the spring guide, which stopped sliding on the guide when the hammer stopped moving forward.... After the shot I measured the gap between the O-ring and the RVA adjusting screw, and that was the amount the valve opened (assuming the valve didn't keep going after the hammer stopped).... The red lines are with the hammer travel set so that it isn't hitting the bumper, but varying the preload.... The more preload, the more the valve opens, and the greater the velocity.... although it is starting to approach a plateau at about 1050 fps.... The blue lines are with the preload set at 1 turn out from coil bind, and the hammer travel before stem contact is varied by recessing the center of the hammer face.... As the face is recessed more, the travel increases, but the maximum valve lift possible before the hammer hits the energy absorbing bumper on the back of the valve decreases.... The hammer starts to contact the bumper at just over 2 turns.... Up to that point, the lift is 0.095" (governed solely by the dynamics of the hammer and valve), and the velocity is basically constant at 1000 fps.... As soon as the amount the valve can lift becomes limited by the hammer hitting the bumper (at about 0.090"?) the velocity starts to drop quickly.... At 5 turns, the valve can't open, and as you can see, the velocity is headed to zero at about that point (or before)....

Bob