A recent client speculated that the frizzen of his Brown Bess flintlock musket was too hard. The issue is not enough spark. Thus, if the frizzen is too hard it would not be effected by the flint and diminshed sparking would be the result.
I made a call to the folks that know everything muzzleloader (Track of the Wolf, http://www.trackofthewolf.com/,763-633-2500), and found that the frizzen of a Brown Bess flintlock musket should be 62-64 HRC (Hardness Rockwell C Scale).
The next step is to test the hardness and see if it is within range.