Having struggled with a few of these over the years, I've come across some of them that have had power issues.
It seems like the valves dont open correctly on some of the guns, and the problem seems to be valve related and not related to the striker, as the problem follows the vale when I switch valves between guns.

The only explanation that seems reasonable to me is that the valve seal has taken a set over time, and that this causes them to stick hard when the striker hits the valve stem

Has anyone on here had any experience with this, or have any ideas on how to fix the problem?