If your machine is 500 psi when you open the trigger you should get 500 psi. We manuacture 500 psi and we deliver 500 psi to the wand.
Secondly to achive this you should be running your wand with 11015 jets.
Yours may be worn and need changing, also your bypass valve may need replacing as it can be bypassing at the wrong pressure.
Kind Regards
Vernon Purcell