Where does the cam/foot of the frizzen rest, in relation to the roller, when the pan is closed? The the cam on the Chambers Late Ketland I have rests at the 3:00 position on the roller. The cam on original roller spring locks I have seen rests at the 1:00 position, on the roller.
IMHO, the higher position of the cam on the roller gives a quicker, snappier kick over to the frizzen. It should give longer flint life too.
God bless