Looks like the steel striking face of the frizzen is a separate piece of steel brazed on to the forged wrought iron frizzen.
Common way to do things then. But on decent quality military locks, and on one pair of Wogdon great coat pistols, the steels were forge welded to the wrought iron frizzens.
Or so it appears to me, examining a few guns in my rather modest collection.
Above lock is on rifle #3, pp 83-84 in John Dillin, showing steel face brazed on to frizzen.