I polished the back side of my trigger bar, my hammer / sear / trigger pins, my hammer strut, and probably something else I forgot. I didn't have the problem of the hammer tilting and rubbing against the frame, so I didn't need to polish the inside of the frame or the rear insert as some people have done. For me, I would say the two single biggest improvements in my DA pull came from going to the 15# hammer spring and the CGW DA roller. I also find that having everything properly cleaned and lubed makes a big difference. After cleaning all the grit and crud out of my frame I spray it out with Hornady Oneshot cleaner and dry lube and it slicks everything up nicely, while not later migrating out and oozing all over my clothing. I also popped the side plate on my S&W J-frame and sprayed it out as well. I don't currently own a trigger scale but according to my son who likes to shoot that revolver quite a bit, it made a big difference in the DA pull.