I've told this story many times.

the coins are stamped out of smooth slugs.

(1) a group are put in to a sand paper base unit and are quickly swished around.

(2) each disk is set in a holding unit and a flat longaded unit in a drill press with a emery cloth rapped around the tip is lowered and just hits the coin to nock-off the burrs.
These two processes were told to me by a elderly gentelmen, along time a go, at the Gaming Expo Show at the Bud Jones site. I was told by to persons to wait and talk the this certain person.