reg gravity feed guns need to beset around 45 psi to blow at 30psi
becuase of the long hose 50ft or 100ft you get a drop from the compressor to the gun

a hvlp gun is like 8-10 psi

be sure to get a regulator for the gun its a little screw on guage that fit into the gun so you can adjust it to get the perfect air pressure.

but rember it also depends on how the paint flows such as base/clear/acrylic/enamal your spread and adjustments on the gun can make it very a few pounds.

Just ne sure to set up a test area and spray a few times untill you get the right settings .