If you use either thin Raw Hide, or lead to wrap the flint, the flint doesn't rebound off the frizzen when it hits. You will know what is happening when you see "chatter marks " on the face of the frizzen begin to appear. I saw one of Larry Pletcher's high speed photos printed and tacked up to one of the rails outside Gunmaker's Hall at Friendship when he was testing flintlocks, and you could clearly see the flint rebounding( or bouncing) off the frizzen when it was wrapped in thicker, Tanned leather.
I discuss this problem at length in my article on Shooting and Tuning Flintlocks, and give a simple test you can do with your own gun to compare lead to leather. See Member Resources on the Index page, then scroll down to " articles, charts, and links." Click on articles, and the second article down is the one I wrote on Shooting and Tuning Flintlocks. I learned this from a late friend, who died 17 years ago today from Multiple Sclerosis, when I was the " Doubting Thomas " about using lead to wrap flints.