I've never found a real good solution to this problem.I have noticed that some brands of equipment are more prone to this trouble.

If in doubt, I'll drill the KO out with a stepper bit. I've also learned to keep at least one pair of reducing washers on the truck for one step down sizing starting with 2 1/2" x 2" down to 3/4" x 1/2".

Few things are harder to put up with than the annoyance of a good example.