I'm using a cheap siphon sand blast gun in mine. I have 170 psi shop air available but I found the media flow is reduced at that pressure. The pressure backs up in the gun. I use a regulator to around 90 psi and get a better media flow.
Drilling out the air jet can cause so much air to flow, you don't get as much suction on the media hose. I put a vacuum gauge on mine to set pressure.