While you can usually get higher velocity from a PCP or a CO2 gun by increasing velocity of the linear hammer by increasing spring tension, it may cause undue wear or failure of the valve stem.
The better quality guns have very sturdy parts, but increasing spring thrust will cut into the mechanisms safety factor.
The Factory specs are approximately (sometimes on the low side) what you can expect from an unaltered gun, with built in safety factor to avoid premature failure and warranty issues.
When converting a CO2 gun to PCP, or vice versa, the spring tension necessary for optimum performance will be different for each power source.
I don't remember the details, but apparently when under that much pressure the differing size of the gas molecules determines just how much gas can pass through the valve in the alotted opening time.
Last edited by Rainbow Demon; January 19, 2013 at 06:50 PM.