So a while back I tried tamping with my left hand. The pain soon ended! But something just wasn't working properly -- my left-tamped shots were always frustratingly inferior to the right-tamped shots that I used to prepare.
I have finally figured out the problem! Like the vast majority of you, I was originally using a right-handed portafilter (see photo below).

But the other day, I received a left-handed portafilter from EPNW (see photo below), and the shots are now coming out just heavenly! I can't believe that I didn't discover this earlier.

Many thanks to Dave and Terry Z for making the left-handed portafilters available.





