I have been dry firing at every opportunity and until my fingers give out. I usually sit there while watching TV and switch between hands as each tires out. Pulling, pulling, pulling. So far, this has only
marginally improved the smoothness of my trigger.
Note that I don't have to pull all the way through to striker release. The gritty section is BEFORE the striker release point. So, I am not firing the striker and racking the slide for each dry fire.
I have three stages to my MP trigger. Initially, through the first third, it is smooth as a good revolver. At about 1/3rd of the way through, I hit a point that most people would think was the stack point where it is about to get harder to pull to fire. However, instead, for mine, this first stop point demarks the beginning of the nasty grit section. 2/3rds of the way through, I exit the grit section at the stack point where the trigger really is at the point that I have to increase pull weight to fire the striker.
So, to work through the grit, I do not have to actually go all the way through a full trigger pull, which helps with the dry firing, at least.