u/InevitableOutcome684

I've bought a new Breville Double boiler machine. Over the past week I notice that I get a different brewing time with almost every shot. Varies from 19 to 30 seconds (mostly in the 19 to 23 sec range). Same beans, same grind and no other settings altered. Coffee shot is similar in weight each time but much more than 1:2. With about 19 gms of coffee I get maybe 50 gms of espresso. Constant 9 bars of pressure. Am I doing something wrong and does the machine work off volume rather than time? Thanks