I've been following this thread since it began, and finally got around to checking out Neolithics: they're now saved to my "favorites"; gonna give 'em a try, with both English and Texas flints.
Thanks for the tip, guys: I'm shooting a Lyman GPR .50, and the stock Lyman lock gives me the runnin' fits. I've tried 4-5 different varieties of flints, in several sizes, and at best, it only gives me 5 or 6 sparks - and scatters those all over the landscape. It often only throws one lonely spark. Yes: I do wipe between each and every shot (attempt).
On the upside, it does give me an opportunity to work on any flinching issues...