I use an ignition file (used to file ignition points) to file off burned areas and to shape the contact, then a thing I have called a flexi-stone (a plastic strip impregnated with grit) to do a final polish. You could also use fine wet sanding paper.

Both contacts need to be clean and smooth.
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'96 855R,'64 PV544 driver, '67 P1800 basket case, '95 855, '95 854, the first three are mine, heh, heh, 485,000 miles put on 9 bricks