If you must polish - use a small dremel and MAAS polishing cream (or mothers). You want to be very careful not to take too much from the ramp, make it uneven, or inadvertently round the lower lip. IF - the HPs are hanging on the lip, could be the pistol just won't run those types - try something with a little more rounded with less opening, go to the Corbon powerball, or use a FMJ. Could also be a slight mis-match between the frame (locking insert I think has a portion of ramp) and bottom of the ramp/barrel. I don't know much about the Sigs, but the locking insert ramp is probably coated with something and should not be polished off??