If you have the Jim Kibler SMR kit rifle that came with a Chambers lock there's a couple of things you might want to consider.
First is that using lead to wrap your flint VOIDS the warranty on your lock.
Second is that in my experience, looking at several Kibler kits so far...the flint that is in the lock when it arrives is a French Amber. Like anything else...opinions vary. Without getting into a discussion of French Amber vs Black English flints I'll just say that unless you just happened to get a bad rock...those French Amber flints have nothing to do with your problem and let it go at that. If changing rocks is all it took to solve your problem...good on you, and ENJOY that new rifle.
In our club, we already have 2 Kibler SMR kit rifles that have been built by members and are showing up at our shoots.
One of them exhibited "issues" with reliability after a few range sessions.
The guy shooting it wasn't cleaning it properly and getting a significant buildup of "crud" on the breechface, preventing reliable ignition. Spending some time with some BP solvents, a scraper, and a breechface brush, along with replacing the rock (which by then was darn near rounded off on what had been the "edge"), got him back in business.