Look at the end of the nozzle – it will have a four or five digit number which gives the angle of spray as the first two digits. The next two or three numbers are the size. (i.e. 15045 is 15° spray angle with 045 size aperture.)
Pressure starts and ends at the nozzle. The volume of water pushed down the hose and forced through the small hole determines the pressure on the gauge. Try taking the nozzle out and then pulling the trigger. You get virtually no pressure registering on the gauge.
The golden rule when diagnosing a loss of pressure is to start at the nozzle and work back to the pump.