I am already aware of grind, and tamp variations,and how they can impact pulling correct shots. The use of quality, recently roasted, beans as well. Having said that, I cannot successfully pull a double shot using a single wall filter with my machine. It will not reach the "espresso range" on the gauge no matter how I adjust the variables. I am able to pull a single shot, using a single wall filter no problem. Any thoughts? All assistance is much appreciated.