This is meant for the less experienced muzzleloaders.
Always remember that when you open the flash hole you not only take away some of the amount of life of a breach plug or vent liner but that over doing the hole size could cause blowback that could be dangerous. It is my personal experience that an over sized flash hole will cause inaccuracy at a point before it causes bad blowback.That's what has happened when a gun looses accuracy and a new breach plug or putting in a vent liner fixes the problem. Sometimes a used gun that is being sold cheap because of inaccuracy can be an easy fix if you know what to look for.