Some good points Stormrider.
Cut gun flints go back a long ways . I seem to recall reading that they were very popular in Germany during the 18th century . I don’t remember right off hand if it was in Greener writings or maybe one of Skertchly
The life of a flint is dictated by a lot of different things .
Lock geometry is a big one . Minor angle distortions can most times be corrected to suitable outcomes by simply changing the angle of the flint in the jaws or flipping the flint over so that its bevel up vs. bevel down OR visa versa .
The other thing is learning to chose quality flints .
Myself , I simply hate ordering flints on line without having a quality reference from another shooter .
Back when I started shooting a lot of flintlocks , we earthier used /made gun spurs or we ordered English flints from Dixie .
The problem was that when you ordered , a lot of times a % of the flints were either un usable or very poor in quality . Today , you can ask and most folks can recommend a person to order from that has a reputation of providing on average a higher 5 of usable and quality flints .
Myself , years back when we heard rumors of Tom Fuller retiring, I jump on it a bought a large quality of his flints . So now about the only thing I buy is French ambers . Which a couple of my rifles prefer over English flints .
So my advice would be , if you have not as of yet don’t it , learn how to chose a quality flint .. Stay away from the cut German agates and two package flints sold at retailers .
Look for consistent color through out the flint . You want good angles and sharp edges . Depending on your lock , you might want a steep back “rib “ and a slopping front rib type flint . Or if you have deep jaws , you might like the double angle .
Myself I search out and chose flat back / toped flints . I have never been able to get an angled top of a common flint to hold correctly in the jaws of my rifles
Next is the placement of the flint to the jaws . A flint that is aloud to move , will not last as long as one that’s solidly mounted . . That means chosing the correct padding for your jaws of your lock .Some folks find lead to be the answer . Myself I use leather . I have tried heavier saddle type leathers . But always seem to come right back to a simple thick piece of chem or Brain tan leather .
Now you chose how to mount the flint . Should it be bevel up or bevel down .
What maters is how the lock sparks the best . The flint should not slam into the frizzen when the lock is fired . So look at how the flint contacts the frizzen .
At half cock “with a short throw lock “ the flint should be just a whisker off the face of the frizzen and pointing at around ¾ up the frizzen face . As you let the cock down , the flint should scrape down the frizzen and shower sparks , NOT try to force itself through the frizzen by slamming into it .
With long fall locks , this is even more important because their ½ and full cocks are so much farther back . There geometry must be true or they will eat flints like not tomorrow .
Once everything is working optimally. IE you have chosen quality flints , set them correctly ….
Now we can look at whats happening to your flints .
Do they wear back quickly .
If so , we then need to look at the edge of the flint . Because the case may be that your getting bounce back from the frizzen and that’s breaking the edge of the flint
But if the case is that the flint is just becoming rounded after repeated shooting then we can look just at the cause of that .
Myself I find that a lot of times this is caused by people who think they have to sharpen their flints all the time and are doing so an a bad angle . Thus resulting in a thick dull edged flint .
IMO if your lock is correct , you have chosen an set the flint correctly ,. Your not getting bounce back , then you should not have to sharpen you flint anymore then just a light clean up , every 7-10 shots .
The angle of that clean up is key . Once that correct angle is achieved , a simple repeated light clean up will slowly work the flint back to the point that one day all you go to move the flint forward and find that you have a small piece that will not hold to the jaws .
The only exception to this when you run into a nubb / hard area in the flint . Then you have to bring out a tool or use heavier more directed blows to get that point knocked off. But once you get the tip of that nubb snapped , then it will also once again go back to only needing light clean up ..
So with the thick flints you have collected .
Take those and set then to the jaws of a padded vice . Either nap the rib back to the flint or file it back using a diamond file. Once you have that angle , then you can go back to knapping the edge while its in the gun