70 shots from ANY flint is incredible & probably depends very much on the timing and 'balance' of the springs in the lock. I would expect that european flints would be the only ones to do that. I know I've gone through the trail on the same flint, then 1/2 way through again, I've decided to change the flint, but I have had to knapp it many times. The trail at that time was 46 rounds.
: Last time out at the range, I used a flint that I'd snapped, perhaps 30 times in the shope during dry-fire practise, when it broke across the edge leaving nly 1/2 an edge. At the range I shot all afternoon with that flint and never had a flash-in-the-pan- probably 50 shots. I was also shooting the .54 flint pistol that day.
: I have found that a piece of steel, 1/8" thick with a "U" notch cut and filed out will remove the thickness of the leading edge of a flint that's been knapped several times. They just seem to get thicker and thicker, and normal knapping just makes them blunter. Using the 'tool' as a rocking pessure device will actually, with practise allow the angle to be lessened and provide even more shots out of a flint. It's easiest to use back home, with the flint in leather padded vice jaws on the work bench.
: This is an adaptation on the "Manton" style knapping tool mentioned in The Rifle Shoppe catolog- probably on-line as well at
www.therifleshoppe.com I started out with a 1/4" notch, but opened it up to about 3/8" X 1/2" deep for large and thicker flints.
Daryl