First off I love this forum and I wish had found it earlier. I mean no disrespect to those here that have years more experience than I but I did want to throw some thought into this...

The chamfering tool I see online scares the the absolute $#i7 out of me! Using a drill? A dremel? What? No, the best way I have found is to use a good solid Bridgeport end mill thats squared in properly on all axis within one-ten-thousandths of an inch (.0001). Then with the extractor KEPT IN PLACE and empty cartridges used in all other chamber holes than that one being cut (rotated each time) to help keep the extractor in place. THEN an actual CHAMFER cutter is used as in the kind used in a machine shop. If this is done by hand it seems ghetto to me. Have a machinist or good gunsmith do it, mine look perfect, uniform, and work great for reloading!!