What surprised me the most was how slow the 7 grain RWS Meisterkugeln were. I wonder if the very viscous grease I applied to the spring is limiting its ability to move the piston fast with light pellets.Perhaps a similar effect is happening with heavy pellets; that piston bounce may be reduced because of a damping force between spring and guide rod inside the piston. In essence, more of the spring's inertia would be coupled to the piston; reducing acceleration in both directions. Just a theory...