Why are my distributor cap terminals burnt?

Check the air gap on all 8 reluctor tips. I used the same type of dist last year & found the reluctor was machined out of round. Rel teeth almost made contact [ misfire when that happens ] with p/up. Found another reluctor & it was ok, uniform air gap.
Also check for shaft wobble, it can close up the gap, especially as rpm increases, from centrifugal force.