my 2 cents.you just got a few bad flints.i had 2 break on me, they were flints from missouri ,white flints.they spark like crazy and are cheaper than fuller flints.

my frizzen is hard and i use lead in jaws.but that was first bad flints in awhile but i seen flints break and most of time it was flint or way it was held in jaws with the top of flint not level as some flints are made.