This simple kit brings some key modifications to the rifle to maximize the power and accuracy potential of the Impact, especially when using slugs. Velocity increases are achieved in large part to the addition of two hammer weight spacers that placed in front of the return spring on the hammer weight guide. This allows for more compression on the hammer spring as well as adding more weight to the overall hammer. Working in harmony with this modification is a lighter valve return spring. This lighter spring allows the valve to stay open slightly longer which allows more air through to propel heavier projectiles like airgun slugs. The kit comes with a .22 caliber pin probe as well as a sleeve that slides over to create a .25 caliber pin probe.